Name
UPDATE -- update rows of a tableSynopsis
[ WITH [ RECURSIVE ] with_query [, ...] ] UPDATE [ ONLY ] table_name [ * ] [ [ AS ] alias ] SET { column_name = { expression | DEFAULT } | ( column_name [, ...] ) = ( { expression | DEFAULT } [, ...] ) | ( column_name [, ...] ) = ( sub-SELECT ) } [, ...] [ FROM from_list ] [ 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 theUPDATE
query. See Section 7.8 and 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. IfONLY
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 theUPDATE
statement must refer to this table asf
notfoo
. 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 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).
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_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 aSELECT
statement. Note that the target table must not appear in thefrom_list
, unless you intend a self-join (in which case it must appear with an alias in thefrom_list
). condition
-
An expression that returns a value of type
boolean
. Only rows for which this expression returnstrue
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 theUPDATE
's target table. Note thatWHERE CURRENT OF
cannot be specified together with a Boolean condition. See DECLARE for more information about using cursors withWHERE 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 bytable_name
or table(s) listed inFROM
. 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');
Update contact names in an accounts table to match the currently assigned salesmen:
UPDATE accounts SET (contact_first_name, contact_last_name) = (SELECT first_name, last_name FROM salesmen WHERE salesmen.id = accounts.sales_id);
A similar result could be accomplished with a join:
UPDATE accounts SET contact_first_name = first_name, contact_last_name = last_name FROM salesmen WHERE salesmen.id = accounts.sales_id;
However, the second query may give unexpected results if salesmen
.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_id
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 column names can be any row-valued expression yielding the correct number of columns. PostgreSQL only allows the source value to be a parenthesized list of expressions (a row constructor) 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
.
Please login to continue.