UPDATE

UPDATE

7

SQL - Language Statements

UPDATE

update rows of a table

\[ WITH \[ RECURSIVE \]

with\_query

\[, \...\] \] UPDATE \[ ONLY \]

table\_name

\[ \* \] \[ \[ AS \]

alias

\] SET {

column\_name

= {

expression

\| DEFAULT } \| (

column\_name

\[, \...\] ) = \[ ROW \] ( {

expression

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

column\_name

\[, \...\] ) = (

sub-SELECT

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

from\_item

\[, \...\] \] \[ WHERE

condition

\| WHERE CURRENT OF

cursor\_name

\] \[ RETURNING \* \|

output\_expression

\[ \[ AS \]

output\_name

\] \[, \...\] \]

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

`UPDATE` changes the values of the specified columns in all rows that
satisfy the condition. Only the columns to be modified need be mentioned
in the `SET` clause; columns not explicitly modified retain their
previous values.

There are two ways to modify a table using information contained in
other tables in the database: using sub-selects, or specifying
additional tables in the `FROM` clause. Which technique is more
appropriate depends on the specific circumstances.

The optional `RETURNING` clause causes `UPDATE` to compute and return
value(s) based on each row actually updated. Any expression using the
table\'s columns, and/or columns of other tables mentioned in `FROM`,
can be computed. The new (post-update) values of the table\'s columns
are used. The syntax of the `RETURNING` list is identical to that of the
output list of `SELECT`.

You must have the `UPDATE` privilege on the table, or at least on the
column(s) that are listed to be updated. You must also have the `SELECT`
privilege on any column whose values are read in the expressions or
condition.

Parameters
==========

with\_query

:   The `WITH` clause allows you to specify one or more subqueries that
    can be referenced by name in the `UPDATE` query. See
    [???](#queries-with) and [???](#sql-select) for details.

table\_name

:   The name (optionally schema-qualified) of the table to update. If
    `ONLY` is specified before the table name, matching rows are updated
    in the named table only. If `ONLY` is not specified, matching rows
    are also updated in any tables inheriting from the named table.
    Optionally, `*` can be specified after the table name to explicitly
    indicate that descendant tables are included.

alias

:   A substitute name for the target table. When an alias is provided,
    it completely hides the actual name of the table. For example, given
    `UPDATE foo AS f`, the remainder of the `UPDATE` statement must
    refer to this table as `f` not `foo`.

column\_name

:   The name of a column in the table named by table\_name. The column
    name can be qualified with a subfield name or array subscript, if
    needed. Do not include the table\'s name in the specification of a
    target column MDASH for example,
    `UPDATE table_name SET table_name.col = 1` is invalid.

expression

:   An expression to assign to the column. The expression can use the
    old values of this and other columns in the table.

`DEFAULT`

:   Set the column to its default value (which will be NULL if no
    specific default expression has been assigned to it). An identity
    column will be set to a new value generated by the associated
    sequence. For a generated column, specifying this is permitted but
    merely specifies the normal behavior of computing the column from
    its generation expression.

sub-SELECT

:   A `SELECT` sub-query that produces as many output columns as are
    listed in the parenthesized column list preceding it. The sub-query
    must yield no more than one row when executed. If it yields one row,
    its column values are assigned to the target columns; if it yields
    no rows, NULL values are assigned to the target columns. The
    sub-query can refer to old values of the current row of the table
    being updated.

from\_item

:   A table expression allowing columns from other tables to appear in
    the `WHERE` condition and update expressions. This uses the same
    syntax as the [`FROM`](#sql-from) clause of a `SELECT` statement;
    for example, an alias for the table name can be specified. Do not
    repeat the target table as a from\_item unless you intend a
    self-join (in which case it must appear with an alias in the
    from\_item).

condition

:   An expression that returns a value of type `boolean`. Only rows for
    which this expression returns `true` will be updated.

cursor\_name

:   The name of the cursor to use in a `WHERE CURRENT OF` condition. The
    row to be updated is the one most recently fetched from this cursor.
    The cursor must be a non-grouping query on the `UPDATE`\'s target
    table. Note that `WHERE CURRENT OF` cannot be specified together
    with a Boolean condition. See [???](#sql-declare) for more
    information about using cursors with `WHERE CURRENT OF`.

output\_expression

:   An expression to be computed and returned by the `UPDATE` command
    after each row is updated. The expression can use any column names
    of the table named by table\_name or table(s) listed in `FROM`.
    Write `*` to return all columns.

output\_name

:   A name to use for a returned column.

Outputs
=======

On successful completion, an `UPDATE` command returns a command tag of
the form

    UPDATE count

The count is the number of rows updated, including matched rows whose
values did not change. Note that the number may be less than the number
of rows that matched the condition when updates were suppressed by a
`BEFORE UPDATE` trigger. If count is 0, no rows were updated by the
query (this is not considered an error).

If the `UPDATE` command contains a `RETURNING` clause, the result will
be similar to that of a `SELECT` statement containing the columns and
values defined in the `RETURNING` list, computed over the row(s) updated
by the command.

Notes
=====

When a `FROM` clause is present, what essentially happens is that the
target table is joined to the tables mentioned in the from\_item list,
and each output row of the join represents an update operation for the
target table. When using `FROM` you should ensure that the join produces
at most one output row for each row to be modified. In other words, a
target row shouldn\'t join to more than one row from the other table(s).
If it does, then only one of the join rows will be used to update the
target row, but which one will be used is not readily predictable.

Because of this indeterminacy, referencing other tables only within
sub-selects is safer, though often harder to read and slower than using
a join.

In the case of a partitioned table, updating a row might cause it to no
longer satisfy the partition constraint of the containing partition. In
that case, if there is some other partition in the partition tree for
which this row satisfies its partition constraint, then the row is moved
to that partition. If there is no such partition, an error will occur.
Behind the scenes, the row movement is actually a `DELETE` and `INSERT`
operation.

There is a possibility that a concurrent `UPDATE` or `DELETE` on the row
being moved will get a serialization failure error. Suppose session 1 is
performing an `UPDATE` on a partition key, and meanwhile a concurrent
session 2 for which this row is visible performs an `UPDATE` or `DELETE`
operation on this row. In such case, session 2\'s `UPDATE` or `DELETE`
will detect the row movement and raise a serialization failure error
(which always returns with an SQLSTATE code \'40001\'). Applications may
wish to retry the transaction if this occurs. In the usual case where
the table is not partitioned, or where there is no row movement, session
2 would have identified the newly updated row and carried out the
`UPDATE`/`DELETE` on this new row version.

Note that while rows can be moved from local partitions to a
foreign-table partition (provided the foreign data wrapper supports
tuple routing), they cannot be moved from a foreign-table partition to
another partition.

An attempt of moving a row from one partition to another will fail if a
foreign key is found to directly reference an ancestor of the source
partition that is not the same as the ancestor that\'s mentioned in the
`UPDATE` query.

Examples
========

Change the word `Drama` to `Dramatic` in the column kind of the table
films:

    UPDATE films SET kind = 'Dramatic' WHERE kind = 'Drama';

Adjust temperature entries and reset precipitation to its default value
in one row of the table weather:

    UPDATE weather SET temp_lo = temp_lo+1, temp_hi = temp_lo+15, prcp = DEFAULT
      WHERE city = 'San Francisco' AND date = '2003-07-03';

Perform the same operation and return the updated entries:

    UPDATE weather SET temp_lo = temp_lo+1, temp_hi = temp_lo+15, prcp = DEFAULT
      WHERE city = 'San Francisco' AND date = '2003-07-03'
      RETURNING temp_lo, temp_hi, prcp;

Use the alternative column-list syntax to do the same update:

    UPDATE weather SET (temp_lo, temp_hi, prcp) = (temp_lo+1, temp_lo+15, DEFAULT)
      WHERE city = 'San Francisco' AND date = '2003-07-03';

Increment the sales count of the salesperson who manages the account for
Acme Corporation, using the `FROM` clause syntax:

    UPDATE employees SET sales_count = sales_count + 1 FROM accounts
      WHERE accounts.name = 'Acme Corporation'
      AND employees.id = accounts.sales_person;

Perform the same operation, using a sub-select in the `WHERE` clause:

    UPDATE employees SET sales_count = sales_count + 1 WHERE id =
      (SELECT sales_person FROM accounts WHERE name = 'Acme Corporation');

Update contact names in an accounts table to match the currently
assigned salespeople:

    UPDATE accounts SET (contact_first_name, contact_last_name) =
        (SELECT first_name, last_name FROM employees
         WHERE employees.id = accounts.sales_person);

A similar result could be accomplished with a join:

    UPDATE accounts SET contact_first_name = first_name,
                        contact_last_name = last_name
      FROM employees WHERE employees.id = accounts.sales_person;

However, the second query may give unexpected results if employees.id is
not a unique key, whereas the first query is guaranteed to raise an
error if there are multiple id matches. Also, if there is no match for a
particular accounts.sales\_person entry, the first query will set the
corresponding name fields to NULL, whereas the second query will not
update that row at all.

Update statistics in a summary table to match the current data:

    UPDATE summary s SET (sum_x, sum_y, avg_x, avg_y) =
        (SELECT sum(x), sum(y), avg(x), avg(y) FROM data d
         WHERE d.group_id = s.group_id);

Attempt to insert a new stock item along with the quantity of stock. If
the item already exists, instead update the stock count of the existing
item. To do this without failing the entire transaction, use savepoints:

    BEGIN;
    -- other operations
    SAVEPOINT sp1;
    INSERT INTO wines VALUES('Chateau Lafite 2003', '24');
    -- Assume the above fails because of a unique key violation,
    -- so now we issue these commands:
    ROLLBACK TO sp1;
    UPDATE wines SET stock = stock + 24 WHERE winename = 'Chateau Lafite 2003';
    -- continue with other operations, and eventually
    COMMIT;

Change the kind column of the table films in the row on which the cursor
`c_films` is currently positioned:

    UPDATE films SET kind = 'Dramatic' WHERE CURRENT OF c_films;

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

This command conforms to the SQL standard, except that the `FROM` and
`RETURNING` clauses are PostgreSQL extensions, as is the ability to use
`WITH` with `UPDATE`.

Some other database systems offer a `FROM` option in which the target
table is supposed to be listed again within `FROM`. That is not how
PostgreSQL interprets `FROM`. Be careful when porting applications that
use this extension.

According to the standard, the source value for a parenthesized sub-list
of target column names can be any row-valued expression yielding the
correct number of columns. PostgreSQL only allows the source value to be
a [row constructor](#sql-syntax-row-constructors) or a sub-`SELECT`. An
individual column\'s updated value can be specified as `DEFAULT` in the
row-constructor case, but not inside a sub-`SELECT`.
