ALTER TABLE

ALTER TABLE

7

SQL - Language Statements

ALTER TABLE

change the definition of a table

ALTER TABLE \[ IF EXISTS \] \[ ONLY \]

name

\[ \* \]

action

\[, \... \] ALTER TABLE \[ IF EXISTS \] \[ ONLY \]

name

\[ \* \] RENAME \[ COLUMN \]

column\_name

TO

new\_column\_name

ALTER TABLE \[ IF EXISTS \] \[ ONLY \]

name

\[ \* \] RENAME CONSTRAINT

constraint\_name

TO

new\_constraint\_name

ALTER TABLE \[ IF EXISTS \]

name

RENAME TO

new\_name

ALTER TABLE \[ IF EXISTS \]

name

SET SCHEMA

new\_schema

ALTER TABLE ALL IN TABLESPACE

name

\[ OWNED BY

role\_name

\[, \... \] \] SET TABLESPACE

new\_tablespace

\[ NOWAIT \] ALTER TABLE \[ IF EXISTS \]

name

ATTACH PARTITION

partition\_name

{ FOR VALUES

partition\_bound\_spec

\| DEFAULT } ALTER TABLE \[ IF EXISTS \]

name

DETACH PARTITION

partition\_name

\[ CONCURRENTLY \| FINALIZE \]

where

action

is one of:

ADD \[ COLUMN \] \[ IF NOT EXISTS \]

column\_name

data\_type

\[ COLLATE

collation

\] \[

column\_constraint

\[ \... \] \] DROP \[ COLUMN \] \[ IF EXISTS \]

column\_name

\[ RESTRICT \| CASCADE \] ALTER \[ COLUMN \]

column\_name

\[ SET DATA \] TYPE

data\_type

\[ COLLATE

collation

\] \[ USING

expression

\] ALTER \[ COLUMN \]

column\_name

SET DEFAULT

expression

ALTER \[ COLUMN \]

column\_name

DROP DEFAULT ALTER \[ COLUMN \]

column\_name

{ SET \| DROP } NOT NULL ALTER \[ COLUMN \]

column\_name

DROP EXPRESSION \[ IF EXISTS \] ALTER \[ COLUMN \]

column\_name

ADD GENERATED { ALWAYS \| BY DEFAULT } AS IDENTITY \[ (

sequence\_options

) \] ALTER \[ COLUMN \]

column\_name

{ SET GENERATED { ALWAYS \| BY DEFAULT } \| SET

sequence\_option

\| RESTART \[ \[ WITH \]

restart

\] } \[\...\] ALTER \[ COLUMN \]

column\_name

DROP IDENTITY \[ IF EXISTS \] ALTER \[ COLUMN \]

column\_name

SET STATISTICS

integer

ALTER \[ COLUMN \]

column\_name

SET (

attribute\_option

=

value

\[, \... \] ) ALTER \[ COLUMN \]

column\_name

RESET (

attribute\_option

\[, \... \] ) ALTER \[ COLUMN \]

column\_name

SET STORAGE { PLAIN \| EXTERNAL \| EXTENDED \| MAIN } ALTER \[ COLUMN \]

column\_name

SET COMPRESSION

compression\_method

ADD

table\_constraint

\[ NOT VALID \] ADD

table\_constraint\_using\_index

ALTER CONSTRAINT

constraint\_name

\[ DEFERRABLE \| NOT DEFERRABLE \] \[ INITIALLY DEFERRED \| INITIALLY
IMMEDIATE \] VALIDATE CONSTRAINT

constraint\_name

DROP CONSTRAINT \[ IF EXISTS \]

constraint\_name

\[ RESTRICT \| CASCADE \] DISABLE TRIGGER \[

trigger\_name

\| ALL \| USER \] ENABLE TRIGGER \[

trigger\_name

\| ALL \| USER \] ENABLE REPLICA TRIGGER

trigger\_name

ENABLE ALWAYS TRIGGER

trigger\_name

DISABLE RULE

rewrite\_rule\_name

ENABLE RULE

rewrite\_rule\_name

ENABLE REPLICA RULE

rewrite\_rule\_name

ENABLE ALWAYS RULE

rewrite\_rule\_name

DISABLE ROW LEVEL SECURITY ENABLE ROW LEVEL SECURITY FORCE ROW LEVEL
SECURITY NO FORCE ROW LEVEL SECURITY CLUSTER ON

index\_name

SET WITHOUT CLUSTER SET WITHOUT OIDS SET ACCESS METHOD

new\_access\_method

SET TABLESPACE

new\_tablespace

SET { LOGGED \| UNLOGGED } SET (

storage\_parameter

\[=

value

\] \[, \... \] ) RESET (

storage\_parameter

\[, \... \] ) INHERIT

parent\_table

NO INHERIT

parent\_table

OF

type\_name

NOT OF OWNER TO {

new\_owner

\| CURRENT\_ROLE \| CURRENT\_USER \| SESSION\_USER } REPLICA IDENTITY {
DEFAULT \| USING INDEX

index\_name

\| FULL \| NOTHING }

and

partition\_bound\_spec

is:

IN (

partition\_bound\_expr

\[, \...\] ) \| FROM ( {

partition\_bound\_expr

\| MINVALUE \| MAXVALUE } \[, \...\] ) TO ( {

partition\_bound\_expr

\| MINVALUE \| MAXVALUE } \[, \...\] ) \| WITH ( MODULUS

numeric\_literal

, REMAINDER

numeric\_literal

)

and

column\_constraint

is:

\[ CONSTRAINT

constraint\_name

\] { NOT NULL \| NULL \| CHECK (

expression

) \[ NO INHERIT \] \| DEFAULT

default\_expr

\| GENERATED ALWAYS AS (

generation\_expr

) STORED \| GENERATED { ALWAYS \| BY DEFAULT } AS IDENTITY \[ (

sequence\_options

) \] \| UNIQUE \[ NULLS \[ NOT \] DISTINCT \]

index\_parameters

\| PRIMARY KEY

index\_parameters

\| REFERENCES

reftable

\[ (

refcolumn

) \] \[ MATCH FULL \| MATCH PARTIAL \| MATCH SIMPLE \] \[ ON DELETE

referential\_action

\] \[ ON UPDATE

referential\_action

\] } \[ DEFERRABLE \| NOT DEFERRABLE \] \[ INITIALLY DEFERRED \|
INITIALLY IMMEDIATE \]

and

table\_constraint

is:

\[ CONSTRAINT

constraint\_name

\] { CHECK (

expression

) \[ NO INHERIT \] \| UNIQUE \[ NULLS \[ NOT \] DISTINCT \] (

column\_name

\[, \... \] )

index\_parameters

\| PRIMARY KEY (

column\_name

\[, \... \] )

index\_parameters

\| EXCLUDE \[ USING

index\_method

\] (

exclude\_element

WITH

operator

\[, \... \] )

index\_parameters

\[ WHERE (

predicate

) \] \| FOREIGN KEY (

column\_name

\[, \... \] ) REFERENCES

reftable

\[ (

refcolumn

\[, \... \] ) \] \[ MATCH FULL \| MATCH PARTIAL \| MATCH SIMPLE \] \[ ON
DELETE

referential\_action

\] \[ ON UPDATE

referential\_action

\] } \[ DEFERRABLE \| NOT DEFERRABLE \] \[ INITIALLY DEFERRED \|
INITIALLY IMMEDIATE \]

and

table\_constraint\_using\_index

is:

\[ CONSTRAINT

constraint\_name

\] { UNIQUE \| PRIMARY KEY } USING INDEX

index\_name

\[ DEFERRABLE \| NOT DEFERRABLE \] \[ INITIALLY DEFERRED \| INITIALLY
IMMEDIATE \]

index\_parameters

in

UNIQUE

,

PRIMARY KEY

, and

EXCLUDE

constraints are:

\[ INCLUDE (

column\_name

\[, \... \] ) \] \[ WITH (

storage\_parameter

\[=

value

\] \[, \... \] ) \] \[ USING INDEX TABLESPACE

tablespace\_name

\]

exclude\_element

in an

EXCLUDE

constraint is:

{

column\_name

\| (

expression

) } \[

opclass

\] \[ ASC \| DESC \] \[ NULLS { FIRST \| LAST } \]

referential\_action

in a

FOREIGN KEY

/

REFERENCES

constraint is:

{ NO ACTION \| RESTRICT \| CASCADE \| SET NULL \[ (

column\_name

\[, \... \] ) \] \| SET DEFAULT \[ (

column\_name

\[, \... \] ) \] }

Description
===========

`ALTER TABLE` changes the definition of an existing table. There are
several subforms described below. Note that the lock level required may
differ for each subform. An `ACCESS EXCLUSIVE` lock is acquired unless
explicitly noted. When multiple subcommands are given, the lock acquired
will be the strictest one required by any subcommand.

`ADD COLUMN [ IF NOT EXISTS ]`

:   This form adds a new column to the table, using the same syntax as
    [`CREATE TABLE`](#sql-createtable). If `IF NOT EXISTS` is specified
    and a column already exists with this name, no error is thrown.

`DROP COLUMN [ IF EXISTS ]`

:   This form drops a column from a table. Indexes and table constraints
    involving the column will be automatically dropped as well.
    Multivariate statistics referencing the dropped column will also be
    removed if the removal of the column would cause the statistics to
    contain data for only a single column. You will need to say
    `CASCADE` if anything outside the table depends on the column, for
    example, foreign key references or views. If `IF EXISTS` is
    specified and the column does not exist, no error is thrown. In this
    case a notice is issued instead.

`SET DATA TYPE`

:   This form changes the type of a column of a table. Indexes and
    simple table constraints involving the column will be automatically
    converted to use the new column type by reparsing the originally
    supplied expression. The optional `COLLATE` clause specifies a
    collation for the new column; if omitted, the collation is the
    default for the new column type. The optional `USING` clause
    specifies how to compute the new column value from the old; if
    omitted, the default conversion is the same as an assignment cast
    from old data type to new. A `USING` clause must be provided if
    there is no implicit or assignment cast from old to new type.

    When this form is used, the column\'s statistics are removed, so
    running [`ANALYZE`](#sql-analyze) on the table afterwards is
    recommended.

`SET`/`DROP DEFAULT`

:   These forms set or remove the default value for a column (where
    removal is equivalent to setting the default value to NULL). The new
    default value will only apply in subsequent `INSERT` or `UPDATE`
    commands; it does not cause rows already in the table to change.

`SET`/`DROP NOT NULL`

:   These forms change whether a column is marked to allow null values
    or to reject null values.

    `SET NOT NULL` may only be applied to a column provided none of the
    records in the table contain a `NULL` value for the column.
    Ordinarily this is checked during the `ALTER TABLE` by scanning the
    entire table; however, if a valid `CHECK` constraint is found which
    proves no `NULL` can exist, then the table scan is skipped.

    If this table is a partition, one cannot perform `DROP NOT NULL` on
    a column if it is marked `NOT NULL` in the parent table. To drop the
    `NOT NULL` constraint from all the partitions, perform
    `DROP NOT NULL` on the parent table. Even if there is no `NOT NULL`
    constraint on the parent, such a constraint can still be added to
    individual partitions, if desired; that is, the children can
    disallow nulls even if the parent allows them, but not the other way
    around.

`DROP EXPRESSION [ IF EXISTS ]`

:   This form turns a stored generated column into a normal base column.
    Existing data in the columns is retained, but future changes will no
    longer apply the generation expression.

    If `DROP EXPRESSION IF EXISTS` is specified and the column is not a
    stored generated column, no error is thrown. In this case a notice
    is issued instead.

`ADD GENERATED { ALWAYS | BY DEFAULT } AS IDENTITY`; `SET GENERATED { ALWAYS | BY DEFAULT }`; `DROP IDENTITY [ IF EXISTS ]`

:   These forms change whether a column is an identity column or change
    the generation attribute of an existing identity column. See
    [`CREATE TABLE`](#sql-createtable) for details. Like `SET DEFAULT`,
    these forms only affect the behavior of subsequent `INSERT` and
    `UPDATE` commands; they do not cause rows already in the table to
    change.

    If `DROP IDENTITY IF EXISTS` is specified and the column is not an
    identity column, no error is thrown. In this case a notice is issued
    instead.

`SET sequence_option`; `RESTART`

:   These forms alter the sequence that underlies an existing identity
    column. sequence\_option is an option supported by
    [`ALTER SEQUENCE`](#sql-altersequence) such as `INCREMENT BY`.

`SET STATISTICS`

:   This form sets the per-column statistics-gathering target for
    subsequent [`ANALYZE`](#sql-analyze) operations. The target can be
    set in the range 0 to 10000; alternatively, set it to -1 to revert
    to using the system default statistics target
    ([???](#guc-default-statistics-target)). For more information on the
    use of statistics by the PostgreSQL query planner, refer to
    [???](#planner-stats).

    `SET STATISTICS` acquires a `SHARE UPDATE EXCLUSIVE` lock.

`SET ( attribute_option = value [, ... ] )`; `RESET ( attribute_option [, ... ] )`

:   This form sets or resets per-attribute options. Currently, the only
    defined per-attribute options are `n_distinct` and
    `n_distinct_inherited`, which override the number-of-distinct-values
    estimates made by subsequent [`ANALYZE`](#sql-analyze) operations.
    `n_distinct` affects the statistics for the table itself, while
    `n_distinct_inherited` affects the statistics gathered for the table
    plus its inheritance children. When set to a positive value,
    `ANALYZE` will assume that the column contains exactly the specified
    number of distinct nonnull values. When set to a negative value,
    which must be greater than or equal to -1, `ANALYZE` will assume
    that the number of distinct nonnull values in the column is linear
    in the size of the table; the exact count is to be computed by
    multiplying the estimated table size by the absolute value of the
    given number. For example, a value of -1 implies that all values in
    the column are distinct, while a value of -0.5 implies that each
    value appears twice on the average. This can be useful when the size
    of the table changes over time, since the multiplication by the
    number of rows in the table is not performed until query planning
    time. Specify a value of 0 to revert to estimating the number of
    distinct values normally. For more information on the use of
    statistics by the PostgreSQL query planner, refer to
    [???](#planner-stats).

    Changing per-attribute options acquires a `SHARE UPDATE EXCLUSIVE`
    lock.

`SET STORAGE` TOAST per-column storage settings

:   This form sets the storage mode for a column. This controls whether
    this column is held inline or in a secondary TOAST table, and
    whether the data should be compressed or not. `PLAIN` must be used
    for fixed-length values such as `integer` and is inline,
    uncompressed. `MAIN` is for inline, compressible data. `EXTERNAL` is
    for external, uncompressed data, and `EXTENDED` is for external,
    compressed data. `EXTENDED` is the default for most data types that
    support non-`PLAIN` storage. Use of `EXTERNAL` will make substring
    operations on very large `text` and `bytea` values run faster, at
    the penalty of increased storage space. Note that `SET STORAGE`
    doesn\'t itself change anything in the table, it just sets the
    strategy to be pursued during future table updates. See
    [???](#storage-toast) for more information.

`SET COMPRESSION compression_method`

:   This form sets the compression method for a column, determining how
    values inserted in future will be compressed (if the storage mode
    permits compression at all). This does not cause the table to be
    rewritten, so existing data may still be compressed with other
    compression methods. If the table is restored with pg\_restore, then
    all values are rewritten with the configured compression method.
    However, when data is inserted from another relation (for example,
    by `INSERT ... SELECT`), values from the source table are not
    necessarily detoasted, so any previously compressed data may retain
    its existing compression method, rather than being recompressed with
    the compression method of the target column. The supported
    compression methods are `pglz` and `lz4`. (`lz4` is available only
    if `--with-lz4` was used when building PostgreSQL.) In addition,
    compression\_method can be `default`, which selects the default
    behavior of consulting the [???](#guc-default-toast-compression)
    setting at the time of data insertion to determine the method to
    use.

`ADD table_constraint [ NOT VALID ]`

:   This form adds a new constraint to a table using the same constraint
    syntax as [`CREATE TABLE`](#sql-createtable), plus the option `NOT
          VALID`, which is currently only allowed for foreign key and
    CHECK constraints.

    Normally, this form will cause a scan of the table to verify that
    all existing rows in the table satisfy the new constraint. But if
    the `NOT VALID` option is used, this potentially-lengthy scan is
    skipped. The constraint will still be enforced against subsequent
    inserts or updates (that is, they\'ll fail unless there is a
    matching row in the referenced table, in the case of foreign keys,
    or they\'ll fail unless the new row matches the specified check
    condition). But the database will not assume that the constraint
    holds for all rows in the table, until it is validated by using the
    `VALIDATE
          CONSTRAINT` option. See [Notes](#sql-altertable-notes) below
    for more information about using the `NOT VALID` option.

    Although most forms of `ADD
          table_constraint` require an `ACCESS EXCLUSIVE` lock, `ADD
          FOREIGN KEY` requires only a `SHARE ROW
          EXCLUSIVE` lock. Note that `ADD FOREIGN KEY` also acquires a
    `SHARE ROW EXCLUSIVE` lock on the referenced table, in addition to
    the lock on the table on which the constraint is declared.

    Additional restrictions apply when unique or primary key constraints
    are added to partitioned tables; see
    [`CREATE TABLE`](#sql-createtable). Also, foreign key constraints on
    partitioned tables may not be declared `NOT VALID` at present.

`ADD table_constraint_using_index`

:   This form adds a new `PRIMARY KEY` or `UNIQUE` constraint to a table
    based on an existing unique index. All the columns of the index will
    be included in the constraint.

    The index cannot have expression columns nor be a partial index.
    Also, it must be a b-tree index with default sort ordering. These
    restrictions ensure that the index is equivalent to one that would
    be built by a regular `ADD PRIMARY KEY` or `ADD UNIQUE` command.

    If `PRIMARY KEY` is specified, and the index\'s columns are not
    already marked `NOT NULL`, then this command will attempt to do
    `ALTER COLUMN SET NOT NULL` against each such column. That requires
    a full table scan to verify the column(s) contain no nulls. In all
    other cases, this is a fast operation.

    If a constraint name is provided then the index will be renamed to
    match the constraint name. Otherwise the constraint will be named
    the same as the index.

    After this command is executed, the index is "owned" by the
    constraint, in the same way as if the index had been built by a
    regular `ADD PRIMARY KEY` or `ADD UNIQUE` command. In particular,
    dropping the constraint will make the index disappear too.

    This form is not currently supported on partitioned tables.

    > **Note**
    >
    > Adding a constraint using an existing index can be helpful in
    > situations where a new constraint needs to be added without
    > blocking table updates for a long time. To do that, create the
    > index using `CREATE INDEX CONCURRENTLY`, and then install it as an
    > official constraint using this syntax. See the example below.

`ALTER CONSTRAINT`

:   This form alters the attributes of a constraint that was previously
    created. Currently only foreign key constraints may be altered.

`VALIDATE CONSTRAINT`

:   This form validates a foreign key or check constraint that was
    previously created as `NOT VALID`, by scanning the table to ensure
    there are no rows for which the constraint is not satisfied. Nothing
    happens if the constraint is already marked valid. (See
    [Notes](#sql-altertable-notes) below for an explanation of the
    usefulness of this command.)

    This command acquires a `SHARE UPDATE EXCLUSIVE` lock.

`DROP CONSTRAINT [ IF EXISTS ]`

:   This form drops the specified constraint on a table, along with any
    index underlying the constraint. If `IF EXISTS` is specified and the
    constraint does not exist, no error is thrown. In this case a notice
    is issued instead.

`DISABLE`/`ENABLE [ REPLICA | ALWAYS ] TRIGGER`

:   These forms configure the firing of trigger(s) belonging to the
    table. A disabled trigger is still known to the system, but is not
    executed when its triggering event occurs. For a deferred trigger,
    the enable status is checked when the event occurs, not when the
    trigger function is actually executed. One can disable or enable a
    single trigger specified by name, or all triggers on the table, or
    only user triggers (this option excludes internally generated
    constraint triggers such as those that are used to implement foreign
    key constraints or deferrable uniqueness and exclusion constraints).
    Disabling or enabling internally generated constraint triggers
    requires superuser privileges; it should be done with caution since
    of course the integrity of the constraint cannot be guaranteed if
    the triggers are not executed.

    The trigger firing mechanism is also affected by the configuration
    variable [???](#guc-session-replication-role). Simply enabled
    triggers (the default) will fire when the replication role is
    "origin" (the default) or "local". Triggers configured as `ENABLE
          REPLICA` will only fire if the session is in "replica" mode,
    and triggers configured as `ENABLE ALWAYS` will fire regardless of
    the current replication role.

    The effect of this mechanism is that in the default configuration,
    triggers do not fire on replicas. This is useful because if a
    trigger is used on the origin to propagate data between tables, then
    the replication system will also replicate the propagated data, and
    the trigger should not fire a second time on the replica, because
    that would lead to duplication. However, if a trigger is used for
    another purpose such as creating external alerts, then it might be
    appropriate to set it to `ENABLE ALWAYS` so that it is also fired on
    replicas.

    This command acquires a `SHARE ROW EXCLUSIVE` lock.

`DISABLE`/`ENABLE [ REPLICA | ALWAYS ] RULE`

:   These forms configure the firing of rewrite rules belonging to the
    table. A disabled rule is still known to the system, but is not
    applied during query rewriting. The semantics are as for
    disabled/enabled triggers. This configuration is ignored for
    `ON SELECT` rules, which are always applied in order to keep views
    working even if the current session is in a non-default replication
    role.

    The rule firing mechanism is also affected by the configuration
    variable [???](#guc-session-replication-role), analogous to triggers
    as described above.

`DISABLE`/`ENABLE ROW LEVEL SECURITY`

:   These forms control the application of row security policies
    belonging to the table. If enabled and no policies exist for the
    table, then a default-deny policy is applied. Note that policies can
    exist for a table even if row-level security is disabled. In this
    case, the policies will *not* be applied and the policies will be
    ignored. See also [`CREATE POLICY`](#sql-createpolicy).

`NO FORCE`/`FORCE ROW LEVEL SECURITY`

:   These forms control the application of row security policies
    belonging to the table when the user is the table owner. If enabled,
    row-level security policies will be applied when the user is the
    table owner. If disabled (the default) then row-level security will
    not be applied when the user is the table owner. See also
    [`CREATE POLICY`](#sql-createpolicy).

`CLUSTER ON`

:   This form selects the default index for future
    [`CLUSTER`](#sql-cluster) operations. It does not actually
    re-cluster the table.

    Changing cluster options acquires a `SHARE UPDATE EXCLUSIVE` lock.

`SET WITHOUT CLUSTER`

:   This form removes the most recently used [`CLUSTER`](#sql-cluster)
    index specification from the table. This affects future cluster
    operations that don\'t specify an index.

    Changing cluster options acquires a `SHARE UPDATE EXCLUSIVE` lock.

`SET WITHOUT OIDS`

:   Backward-compatible syntax for removing the `oid` system column. As
    `oid` system columns cannot be added anymore, this never has an
    effect.

`SET ACCESS METHOD`

:   This form changes the access method of the table by rewriting it.
    See [???](#tableam) for more information.

`SET TABLESPACE`

:   This form changes the table\'s tablespace to the specified
    tablespace and moves the data file(s) associated with the table to
    the new tablespace. Indexes on the table, if any, are not moved; but
    they can be moved separately with additional `SET TABLESPACE`
    commands. When applied to a partitioned table, nothing is moved, but
    any partitions created afterwards with `CREATE TABLE PARTITION OF`
    will use that tablespace, unless overridden by a `TABLESPACE`
    clause.

    All tables in the current database in a tablespace can be moved by
    using the `ALL IN TABLESPACE` form, which will lock all tables to be
    moved first and then move each one. This form also supports
    `OWNED BY`, which will only move tables owned by the roles
    specified. If the `NOWAIT` option is specified then the command will
    fail if it is unable to acquire all of the locks required
    immediately. Note that system catalogs are not moved by this
    command; use `ALTER DATABASE` or explicit `ALTER TABLE` invocations
    instead if desired. The `information_schema` relations are not
    considered part of the system catalogs and will be moved. See also
    [`CREATE TABLESPACE`](#sql-createtablespace).

`SET { LOGGED | UNLOGGED }`

:   This form changes the table from unlogged to logged or vice-versa
    (see [???](#sql-createtable-unlogged)). It cannot be applied to a
    temporary table.

    This also changes the persistence of any sequences linked to the
    table (for identity or serial columns). However, it is also possible
    to change the persistence of such sequences separately.

`SET ( storage_parameter [= value] [, ... ] )`

:   This form changes one or more storage parameters for the table. See
    [???](#sql-createtable-storage-parameters) in the
    [`CREATE TABLE`](#sql-createtable) documentation for details on the
    available parameters. Note that the table contents will not be
    modified immediately by this command; depending on the parameter you
    might need to rewrite the table to get the desired effects. That can
    be done with [`VACUUM
          FULL`](#sql-vacuum), [`CLUSTER`](#sql-cluster) or one of the
    forms of `ALTER TABLE` that forces a table rewrite. For planner
    related parameters, changes will take effect from the next time the
    table is locked so currently executing queries will not be affected.

    `SHARE UPDATE EXCLUSIVE` lock will be taken for fillfactor, toast
    and autovacuum storage parameters, as well as the planner parameter
    `parallel_workers`.

`RESET ( storage_parameter [, ... ] )`

:   This form resets one or more storage parameters to their defaults.
    As with `SET`, a table rewrite might be needed to update the table
    entirely.

`INHERIT parent_table`

:   This form adds the target table as a new child of the specified
    parent table. Subsequently, queries against the parent will include
    records of the target table. To be added as a child, the target
    table must already contain all the same columns as the parent (it
    could have additional columns, too). The columns must have matching
    data types, and if they have `NOT NULL` constraints in the parent
    then they must also have `NOT NULL` constraints in the child.

    There must also be matching child-table constraints for all `CHECK`
    constraints of the parent, except those marked non-inheritable (that
    is, created with `ALTER TABLE ... ADD CONSTRAINT ... NO INHERIT`) in
    the parent, which are ignored; all child-table constraints matched
    must not be marked non-inheritable. Currently `UNIQUE`,
    `PRIMARY KEY`, and `FOREIGN KEY` constraints are not considered, but
    this might change in the future.

`NO INHERIT parent_table`

:   This form removes the target table from the list of children of the
    specified parent table. Queries against the parent table will no
    longer include records drawn from the target table.

`OF type_name`

:   This form links the table to a composite type as though `CREATE
          TABLE OF` had formed it. The table\'s list of column names and
    types must precisely match that of the composite type. The table
    must not inherit from any other table. These restrictions ensure
    that `CREATE TABLE OF` would permit an equivalent table definition.

`NOT OF`

:   This form dissociates a typed table from its type.

`OWNER TO`

:   This form changes the owner of the table, sequence, view,
    materialized view, or foreign table to the specified user.

`REPLICA IDENTITY`

:   This form changes the information which is written to the
    write-ahead log to identify rows which are updated or deleted. In
    most cases, the old value of each column is only logged if it
    differs from the new value; however, if the old value is stored
    externally, it is always logged regardless of whether it changed.
    This option has no effect except when logical replication is in use.

    `DEFAULT`

    :   Records the old values of the columns of the primary key, if
        any. This is the default for non-system tables.

    `USING INDEX index_name`

    :   Records the old values of the columns covered by the named
        index, that must be unique, not partial, not deferrable, and
        include only columns marked `NOT NULL`. If this index is
        dropped, the behavior is the same as `NOTHING`.

    `FULL`

    :   Records the old values of all columns in the row.

    `NOTHING`

    :   Records no information about the old row. This is the default
        for system tables.

`RENAME`

:   The `RENAME` forms change the name of a table (or an index,
    sequence, view, materialized view, or foreign table), the name of an
    individual column in a table, or the name of a constraint of the
    table. When renaming a constraint that has an underlying index, the
    index is renamed as well. There is no effect on the stored data.

`SET SCHEMA`

:   This form moves the table into another schema. Associated indexes,
    constraints, and sequences owned by table columns are moved as well.

`ATTACH PARTITION partition_name { FOR VALUES partition_bound_spec | DEFAULT }`

:   This form attaches an existing table (which might itself be
    partitioned) as a partition of the target table. The table can be
    attached as a partition for specific values using `FOR VALUES` or as
    a default partition by using `DEFAULT`. For each index in the target
    table, a corresponding one will be created in the attached table;
    or, if an equivalent index already exists, it will be attached to
    the target table\'s index, as if `ALTER INDEX ATTACH PARTITION` had
    been executed. Note that if the existing table is a foreign table,
    it is currently not allowed to attach the table as a partition of
    the target table if there are `UNIQUE` indexes on the target table.
    (See also [???](#sql-createforeigntable).) For each user-defined
    row-level trigger that exists in the target table, a corresponding
    one is created in the attached table.

    A partition using `FOR VALUES` uses same syntax for
    partition\_bound\_spec as [`CREATE TABLE`](#sql-createtable). The
    partition bound specification must correspond to the partitioning
    strategy and partition key of the target table. The table to be
    attached must have all the same columns as the target table and no
    more; moreover, the column types must also match. Also, it must have
    all the `NOT NULL` and `CHECK` constraints of the target table.
    Currently `FOREIGN KEY` constraints are not considered. `UNIQUE` and
    `PRIMARY KEY` constraints from the parent table will be created in
    the partition, if they don\'t already exist. If any of the `CHECK`
    constraints of the table being attached are marked `NO INHERIT`, the
    command will fail; such constraints must be recreated without the
    `NO INHERIT` clause.

    If the new partition is a regular table, a full table scan is
    performed to check that existing rows in the table do not violate
    the partition constraint. It is possible to avoid this scan by
    adding a valid `CHECK` constraint to the table that allows only rows
    satisfying the desired partition constraint before running this
    command. The `CHECK` constraint will be used to determine that the
    table need not be scanned to validate the partition constraint. This
    does not work, however, if any of the partition keys is an
    expression and the partition does not accept `NULL` values. If
    attaching a list partition that will not accept `NULL` values, also
    add `NOT NULL` constraint to the partition key column, unless it\'s
    an expression.

    If the new partition is a foreign table, nothing is done to verify
    that all the rows in the foreign table obey the partition
    constraint. (See the discussion in [???](#sql-createforeigntable)
    about constraints on the foreign table.)

    When a table has a default partition, defining a new partition
    changes the partition constraint for the default partition. The
    default partition can\'t contain any rows that would need to be
    moved to the new partition, and will be scanned to verify that none
    are present. This scan, like the scan of the new partition, can be
    avoided if an appropriate `CHECK` constraint is present. Also like
    the scan of the new partition, it is always skipped when the default
    partition is a foreign table.

    Attaching a partition acquires a `SHARE UPDATE EXCLUSIVE` lock on
    the parent table, in addition to the `ACCESS EXCLUSIVE` locks on the
    table being attached and on the default partition (if any).

    Further locks must also be held on all sub-partitions if the table
    being attached is itself a partitioned table. Likewise if the
    default partition is itself a partitioned table. The locking of the
    sub-partitions can be avoided by adding a `CHECK` constraint as
    described in [???](#ddl-partitioning-declarative-maintenance).

`DETACH PARTITION partition_name [ CONCURRENTLY | FINALIZE ]`

:   This form detaches the specified partition of the target table. The
    detached partition continues to exist as a standalone table, but no
    longer has any ties to the table from which it was detached. Any
    indexes that were attached to the target table\'s indexes are
    detached. Any triggers that were created as clones of those in the
    target table are removed. `SHARE` lock is obtained on any tables
    that reference this partitioned table in foreign key constraints.

    If `CONCURRENTLY` is specified, it runs using a reduced lock level
    to avoid blocking other sessions that might be accessing the
    partitioned table. In this mode, two transactions are used
    internally. During the first transaction, a `SHARE UPDATE EXCLUSIVE`
    lock is taken on both parent table and partition, and the partition
    is marked as undergoing detach; at that point, the transaction is
    committed and all other transactions using the partitioned table are
    waited for. Once all those transactions have completed, the second
    transaction acquires `SHARE UPDATE EXCLUSIVE` on the partitioned
    table and `ACCESS EXCLUSIVE` on the partition, and the detach
    process completes. A `CHECK` constraint that duplicates the
    partition constraint is added to the partition. `CONCURRENTLY`
    cannot be run in a transaction block and is not allowed if the
    partitioned table contains a default partition.

    If `FINALIZE` is specified, a previous `DETACH CONCURRENTLY`
    invocation that was canceled or interrupted is completed. At most
    one partition in a partitioned table can be pending detach at a
    time.

All the forms of ALTER TABLE that act on a single table, except
`RENAME`, `SET SCHEMA`, `ATTACH PARTITION`, and `DETACH PARTITION` can
be combined into a list of multiple alterations to be applied together.
For example, it is possible to add several columns and/or alter the type
of several columns in a single command. This is particularly useful with
large tables, since only one pass over the table need be made.

You must own the table to use `ALTER TABLE`. To change the schema or
tablespace of a table, you must also have `CREATE` privilege on the new
schema or tablespace. To add the table as a new child of a parent table,
you must own the parent table as well. Also, to attach a table as a new
partition of the table, you must own the table being attached. To alter
the owner, you must also be a direct or indirect member of the new
owning role, and that role must have `CREATE` privilege on the table\'s
schema. (These restrictions enforce that altering the owner doesn\'t do
anything you couldn\'t do by dropping and recreating the table. However,
a superuser can alter ownership of any table anyway.) To add a column or
alter a column type or use the `OF` clause, you must also have `USAGE`
privilege on the data type.

Parameters
==========

`IF EXISTS`

:   Do not throw an error if the table does not exist. A notice is
    issued in this case.

name

:   The name (optionally schema-qualified) of an existing table to
    alter. If `ONLY` is specified before the table name, only that table
    is altered. If `ONLY` is not specified, the table and all its
    descendant tables (if any) are altered. Optionally, `*` can be
    specified after the table name to explicitly indicate that
    descendant tables are included.

column\_name

:   Name of a new or existing column.

new\_column\_name

:   New name for an existing column.

new\_name

:   New name for the table.

data\_type

:   Data type of the new column, or new data type for an existing
    column.

table\_constraint

:   New table constraint for the table.

constraint\_name

:   Name of a new or existing constraint.

`CASCADE`

:   Automatically drop objects that depend on the dropped column or
    constraint (for example, views referencing the column), and in turn
    all objects that depend on those objects (see [???](#ddl-depend)).

`RESTRICT`

:   Refuse to drop the column or constraint if there are any dependent
    objects. This is the default behavior.

trigger\_name

:   Name of a single trigger to disable or enable.

`ALL`

:   Disable or enable all triggers belonging to the table. (This
    requires superuser privilege if any of the triggers are internally
    generated constraint triggers such as those that are used to
    implement foreign key constraints or deferrable uniqueness and
    exclusion constraints.)

`USER`

:   Disable or enable all triggers belonging to the table except for
    internally generated constraint triggers such as those that are used
    to implement foreign key constraints or deferrable uniqueness and
    exclusion constraints.

index\_name

:   The name of an existing index.

storage\_parameter

:   The name of a table storage parameter.

value

:   The new value for a table storage parameter. This might be a number
    or a word depending on the parameter.

parent\_table

:   A parent table to associate or de-associate with this table.

new\_owner

:   The user name of the new owner of the table.

new\_access\_method

:   The name of the access method to which the table will be converted.

new\_tablespace

:   The name of the tablespace to which the table will be moved.

new\_schema

:   The name of the schema to which the table will be moved.

partition\_name

:   The name of the table to attach as a new partition or to detach from
    this table.

partition\_bound\_spec

:   The partition bound specification for a new partition. Refer to
    [???](#sql-createtable) for more details on the syntax of the same.

Notes {#sql-altertable-notes}
=====

The key word `COLUMN` is noise and can be omitted.

When a column is added with `ADD COLUMN` and a non-volatile `DEFAULT` is
specified, the default is evaluated at the time of the statement and the
result stored in the table\'s metadata. That value will be used for the
column for all existing rows. If no `DEFAULT` is specified, NULL is
used. In neither case is a rewrite of the table required.

Adding a column with a volatile `DEFAULT` or changing the type of an
existing column will require the entire table and its indexes to be
rewritten. As an exception, when changing the type of an existing
column, if the `USING` clause does not change the column contents and
the old type is either binary coercible to the new type or an
unconstrained domain over the new type, a table rewrite is not needed.
However, indexes must always be rebuilt unless the system can verify
that the new index would be logically equivalent to the existing one.
For example, if the collation for a column has been changed an index
rebuild is always required because the new sort order might be
different. However, in the absence of a collation change, a column can
be changed from `text` to `varchar` (or vice versa) without rebuilding
the indexes because these data types sort identically. Table and/or
index rebuilds may take a significant amount of time for a large table;
and will temporarily require as much as double the disk space.

Adding a `CHECK` or `NOT NULL` constraint requires scanning the table to
verify that existing rows meet the constraint, but does not require a
table rewrite.

Similarly, when attaching a new partition it may be scanned to verify
that existing rows meet the partition constraint.

The main reason for providing the option to specify multiple changes in
a single `ALTER TABLE` is that multiple table scans or rewrites can
thereby be combined into a single pass over the table.

Scanning a large table to verify a new foreign key or check constraint
can take a long time, and other updates to the table are locked out
until the `ALTER TABLE ADD CONSTRAINT` command is committed. The main
purpose of the `NOT VALID` constraint option is to reduce the impact of
adding a constraint on concurrent updates. With `NOT VALID`, the
`ADD CONSTRAINT` command does not scan the table and can be committed
immediately. After that, a `VALIDATE
    CONSTRAINT` command can be issued to verify that existing rows
satisfy the constraint. The validation step does not need to lock out
concurrent updates, since it knows that other transactions will be
enforcing the constraint for rows that they insert or update; only
pre-existing rows need to be checked. Hence, validation acquires only a
`SHARE UPDATE EXCLUSIVE` lock on the table being altered. (If the
constraint is a foreign key then a `ROW
    SHARE` lock is also required on the table referenced by the
constraint.) In addition to improving concurrency, it can be useful to
use `NOT VALID` and `VALIDATE
    CONSTRAINT` in cases where the table is known to contain
pre-existing violations. Once the constraint is in place, no new
violations can be inserted, and the existing problems can be corrected
at leisure until `VALIDATE CONSTRAINT` finally succeeds.

The `DROP COLUMN` form does not physically remove the column, but simply
makes it invisible to SQL operations. Subsequent insert and update
operations in the table will store a null value for the column. Thus,
dropping a column is quick but it will not immediately reduce the
on-disk size of your table, as the space occupied by the dropped column
is not reclaimed. The space will be reclaimed over time as existing rows
are updated.

To force immediate reclamation of space occupied by a dropped column,
you can execute one of the forms of `ALTER TABLE` that performs a
rewrite of the whole table. This results in reconstructing each row with
the dropped column replaced by a null value.

The rewriting forms of `ALTER TABLE` are not MVCC-safe. After a table
rewrite, the table will appear empty to concurrent transactions, if they
are using a snapshot taken before the rewrite occurred. See
[???](#mvcc-caveats) for more details.

The `USING` option of `SET DATA TYPE` can actually specify any
expression involving the old values of the row; that is, it can refer to
other columns as well as the one being converted. This allows very
general conversions to be done with the `SET DATA TYPE` syntax. Because
of this flexibility, the `USING` expression is not applied to the
column\'s default value (if any); the result might not be a constant
expression as required for a default. This means that when there is no
implicit or assignment cast from old to new type, `SET DATA TYPE` might
fail to convert the default even though a `USING` clause is supplied. In
such cases, drop the default with `DROP DEFAULT`, perform the `ALTER
    TYPE`, and then use `SET DEFAULT` to add a suitable new default.
Similar considerations apply to indexes and constraints involving the
column.

If a table has any descendant tables, it is not permitted to add,
rename, or change the type of a column in the parent table without doing
the same to the descendants. This ensures that the descendants always
have columns matching the parent. Similarly, a `CHECK` constraint cannot
be renamed in the parent without also renaming it in all descendants, so
that `CHECK` constraints also match between the parent and its
descendants. (That restriction does not apply to index-based
constraints, however.) Also, because selecting from the parent also
selects from its descendants, a constraint on the parent cannot be
marked valid unless it is also marked valid for those descendants. In
all of these cases, `ALTER TABLE
    ONLY` will be rejected.

A recursive `DROP COLUMN` operation will remove a descendant table\'s
column only if the descendant does not inherit that column from any
other parents and never had an independent definition of the column. A
nonrecursive `DROP
    COLUMN` (i.e., `ALTER TABLE ONLY ... DROP
    COLUMN`) never removes any descendant columns, but instead marks
them as independently defined rather than inherited. A nonrecursive
`DROP COLUMN` command will fail for a partitioned table, because all
partitions of a table must have the same columns as the partitioning
root.

The actions for identity columns (`ADD
    GENERATED`, `SET` etc., `DROP
    IDENTITY`), as well as the actions `TRIGGER`, `CLUSTER`, `OWNER`,
and `TABLESPACE` never recurse to descendant tables; that is, they
always act as though `ONLY` were specified. Adding a constraint recurses
only for `CHECK` constraints that are not marked `NO INHERIT`.

Changing any part of a system catalog table is not permitted.

Refer to [???](#sql-createtable) for a further description of valid
parameters. [???](#ddl) has further information on inheritance.

Examples
========

To add a column of type `varchar` to a table:

    ALTER TABLE distributors ADD COLUMN address varchar(30);

That will cause all existing rows in the table to be filled with null
values for the new column.

To add a column with a non-null default:

    ALTER TABLE measurements
      ADD COLUMN mtime timestamp with time zone DEFAULT now();

Existing rows will be filled with the current time as the value of the
new column, and then new rows will receive the time of their insertion.

To add a column and fill it with a value different from the default to
be used later:

    ALTER TABLE transactions
      ADD COLUMN status varchar(30) DEFAULT 'old',
      ALTER COLUMN status SET default 'current';

Existing rows will be filled with `old`, but then the default for
subsequent commands will be `current`. The effects are the same as if
the two sub-commands had been issued in separate `ALTER TABLE` commands.

To drop a column from a table:

    ALTER TABLE distributors DROP COLUMN address RESTRICT;

To change the types of two existing columns in one operation:

    ALTER TABLE distributors
        ALTER COLUMN address TYPE varchar(80),
        ALTER COLUMN name TYPE varchar(100);

To change an integer column containing Unix timestamps to `timestamp
   with time zone` via a `USING` clause:

    ALTER TABLE foo
        ALTER COLUMN foo_timestamp SET DATA TYPE timestamp with time zone
        USING
            timestamp with time zone 'epoch' + foo_timestamp * interval '1 second';

The same, when the column has a default expression that won\'t
automatically cast to the new data type:

    ALTER TABLE foo
        ALTER COLUMN foo_timestamp DROP DEFAULT,
        ALTER COLUMN foo_timestamp TYPE timestamp with time zone
        USING
            timestamp with time zone 'epoch' + foo_timestamp * interval '1 second',
        ALTER COLUMN foo_timestamp SET DEFAULT now();

To rename an existing column:

    ALTER TABLE distributors RENAME COLUMN address TO city;

To rename an existing table:

    ALTER TABLE distributors RENAME TO suppliers;

To rename an existing constraint:

    ALTER TABLE distributors RENAME CONSTRAINT zipchk TO zip_check;

To add a not-null constraint to a column:

    ALTER TABLE distributors ALTER COLUMN street SET NOT NULL;

To remove a not-null constraint from a column:

    ALTER TABLE distributors ALTER COLUMN street DROP NOT NULL;

To add a check constraint to a table and all its children:

    ALTER TABLE distributors ADD CONSTRAINT zipchk CHECK (char_length(zipcode) = 5);

To add a check constraint only to a table and not to its children:

    ALTER TABLE distributors ADD CONSTRAINT zipchk CHECK (char_length(zipcode) = 5) NO INHERIT;

(The check constraint will not be inherited by future children, either.)

To remove a check constraint from a table and all its children:

    ALTER TABLE distributors DROP CONSTRAINT zipchk;

To remove a check constraint from one table only:

    ALTER TABLE ONLY distributors DROP CONSTRAINT zipchk;

(The check constraint remains in place for any child tables.)

To add a foreign key constraint to a table:

    ALTER TABLE distributors ADD CONSTRAINT distfk FOREIGN KEY (address) REFERENCES addresses (address);

To add a foreign key constraint to a table with the least impact on
other work:

    ALTER TABLE distributors ADD CONSTRAINT distfk FOREIGN KEY (address) REFERENCES addresses (address) NOT VALID;
    ALTER TABLE distributors VALIDATE CONSTRAINT distfk;

To add a (multicolumn) unique constraint to a table:

    ALTER TABLE distributors ADD CONSTRAINT dist_id_zipcode_key UNIQUE (dist_id, zipcode);

To add an automatically named primary key constraint to a table, noting
that a table can only ever have one primary key:

    ALTER TABLE distributors ADD PRIMARY KEY (dist_id);

To move a table to a different tablespace:

    ALTER TABLE distributors SET TABLESPACE fasttablespace;

To move a table to a different schema:

    ALTER TABLE myschema.distributors SET SCHEMA yourschema;

To recreate a primary key constraint, without blocking updates while the
index is rebuilt:

    CREATE UNIQUE INDEX CONCURRENTLY dist_id_temp_idx ON distributors (dist_id);
    ALTER TABLE distributors DROP CONSTRAINT distributors_pkey,
        ADD CONSTRAINT distributors_pkey PRIMARY KEY USING INDEX dist_id_temp_idx;

To attach a partition to a range-partitioned table:

    ALTER TABLE measurement
        ATTACH PARTITION measurement_y2016m07 FOR VALUES FROM ('2016-07-01') TO ('2016-08-01');

To attach a partition to a list-partitioned table:

    ALTER TABLE cities
        ATTACH PARTITION cities_ab FOR VALUES IN ('a', 'b');

To attach a partition to a hash-partitioned table:

    ALTER TABLE orders
        ATTACH PARTITION orders_p4 FOR VALUES WITH (MODULUS 4, REMAINDER 3);

To attach a default partition to a partitioned table:

    ALTER TABLE cities
        ATTACH PARTITION cities_partdef DEFAULT;

To detach a partition from a partitioned table:

    ALTER TABLE measurement
        DETACH PARTITION measurement_y2015m12;

Compatibility
=============

The forms `ADD` (without `USING INDEX`), `DROP [COLUMN]`,
`DROP IDENTITY`, `RESTART`, `SET DEFAULT`, `SET DATA TYPE` (without
`USING`), `SET GENERATED`, and `SET sequence_option` conform with the
SQL standard. The other forms are PostgreSQL extensions of the SQL
standard. Also, the ability to specify more than one manipulation in a
single `ALTER TABLE` command is an extension.

`ALTER TABLE DROP COLUMN` can be used to drop the only column of a
table, leaving a zero-column table. This is an extension of SQL, which
disallows zero-column tables.

See Also
========
