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UPDATE

Name

UPDATE  --  update rows of a table

Synopsis

UPDATE [ ONLY ] table SET col = expression [, ...]
    [ FROM fromlist ]
    [ WHERE condition ]
  

Inputs

table

The name (optionally schema-qualified) of an existing table. If ONLY is specified, only that table is updated. If ONLY is not specified, the table and all its descendant tables (if any) are updated. * can be appended to the table name to indicate that descendant tables are to be scanned, but in the current version, this is the default behavior. (In releases before 7.1, ONLY was the default behavior.) The default can be altered by changing the SQL_INHERITANCE configuration option.

column

The name of a column in table.

expression

A valid expression or value to assign to column.

fromlist

A PostgreSQL non-standard extension to allow columns from other tables to appear in the WHERE condition.

condition

Refer to the SELECT statement for a further description of the WHERE clause.

Outputs

UPDATE #

Message returned if successful. The # means the number of rows updated. If # is 0 no rows are updated.

Description

UPDATE changes the values of the columns specified for all rows which satisfy condition. Only the columns to be modified need appear as columns in the statement.

Array references use the same syntax found in SELECT. That is, either single array elements, a range of array elements or the entire array may be replaced with a single query.

You must have write access to the table in order to modify it, as well as read access to any table whose values are mentioned in the WHERE condition.

By default UPDATE will update tuples in the table specified and all its sub-tables. If you wish to only update the specific table mentioned, you should use the ONLY clause.

Usage

Change word Drama with Dramatic on column kind:

UPDATE films 
SET kind = 'Dramatic' 
WHERE kind = 'Drama';
SELECT * 
FROM films 
WHERE kind = 'Dramatic' OR kind = 'Drama';

 code  |     title     | did | date_prod  |   kind   | len
-------+---------------+-----+------------+----------+-------
 BL101 | The Third Man | 101 | 1949-12-23 | Dramatic | 01:44
 P_302 | Becket        | 103 | 1964-02-03 | Dramatic | 02:28
 M_401 | War and Peace | 104 | 1967-02-12 | Dramatic | 05:57
 T_601 | Yojimbo       | 106 | 1961-06-16 | Dramatic | 01:50
 DA101 | Das Boot      | 110 | 1981-11-11 | Dramatic | 02:29

Compatibility

SQL92

SQL92 defines a different syntax for the positioned UPDATE statement:

UPDATE table SET column = expression [, ...]
    WHERE CURRENT OF cursor
    

where cursor identifies an open cursor.

Comments


Dec. 19, 2002, 3:25 a.m.

A lot of people don't know this, but the where expression allows subselects. This would generally be a better way to write back data constructed from a multiple table query than to do an iterative loop in code. IMHO, this is a much more genrally useful application of subselects than complex queries. (select statements can be written to avoid subselects, update statements can't). Contrast mysql.

Example:
update b set value = 'changed' where b.aid in (select id from a where afield = 'filter_condition');

A more automatic approach would be to use views (which requires learning & dealing with the rule system) or triggers/stored procedures. I generally use views and sps but not triggers. You just can't beat an update for simplicity though. My point is that doing an interative loop in php or some other client language is usually not the best approach.


Feb. 18, 2003, 11:28 a.m.

It should probably be noted here that the FROM clause also makes the foreign tables available to the expression part of the SET clause.


July 19, 2004, 3:35 p.m.

update-from example that copies one column between tables using another as key.

update
table_a
set
column_1 = table_b.column_1
from
table_b
where
table_a.column_2 = table_b.column_2;

HTH.

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