UPDATE(7) PostgreSQL 9.3.2 Documentation UPDATE(7)NAMEUPDATE - update rows of a table
SYNOPSIS
[ WITH [ RECURSIVE ] with_query [, ...] ]
UPDATE [ ONLY ] table_name [ * ] [ [ AS ] alias ]
SET { column_name = { expression | DEFAULT } |
( column_name [, ...] ) = ( { expression | DEFAULT } [, ...] ) } [, ...]
[ FROM from_list ]
[ WHERE condition | WHERE CURRENT OF cursor_name ]
[ RETURNING * | output_expression [ [ AS ] output_name ] [, ...] ]
DESCRIPTIONUPDATE 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 Section 7.8,
“WITH Queries (Common Table Expressions)”, in the documentation and
SELECT(7) 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 — for example, UPDATE tab SET tab.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).
from_list
A list of table expressions, allowing columns from other tables to
appear in the WHERE condition and the update expressions. This is
similar to the list of tables that can be specified in the FROM
Clause of a SELECT statement. Note that the target table must not
appear in the from_list, unless you intend a self-join (in which
case it must appear with an alias in the from_list).
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 DECLARE(7) 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_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.
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');
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.
According to the standard, the column-list syntax should allow a list
of columns to be assigned from a single row-valued expression, such as
a sub-select:
UPDATE accounts SET (contact_last_name, contact_first_name) =
(SELECT last_name, first_name FROM salesmen
WHERE salesmen.id = accounts.sales_id);
This is not currently implemented — the source must be a list of
independent expressions.
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.
PostgreSQL 9.3.2 2013 UPDATE(7)
