PostgreSQL 7.4 Documentation
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# UPDATE

## Name

UPDATE -- update rows of a table

## Synopsis

    UPDATE [ ONLY ] table SET column = { expression | DEFAULT } [, ...]
        [ FROM fromlist ]
        [ WHERE condition ]

## 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 statement; columns not explicitly SET retain their previous values.

By default, `UPDATE` will update rows in the specified table and all its subtables. If you wish to only update the specific table mentioned, you must use the ONLY clause.

You must have the UPDATE privilege on the table to update it, as well as the SELECT privilege to any table whose values are read in the expressions or condition.

## Parameters

table

  The name (optionally schema-qualified) of the table to update.

column

  The name of a column in table.

expression

  An expression to assign to the column. The expression may 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).

fromlist

  A list of table expressions, allowing columns from other tables to appear in the WHERE condition and the update expressions.

condition

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

## Outputs

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

    UPDATE count

The count is the number of rows updated. If count is 0, no rows matched the condition (this is not considered an error).

## 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';

## Compatibility

This command conforms to the SQL standard. The FROM clause is a PostgreSQL extension.

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