NAME

       UPDATE - update rows of a table

SYNOPSIS

       [ 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 Section 7.8 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 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_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 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 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_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. Since there is no provision to move the row to the partition
       appropriate to the new value of its partitioning key, an error will occur in this case.
       This can also happen when updating a partition directly.

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 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 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.