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UPDATE

   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 [ WITH ( { OLD | NEW } AS output_alias [, ...] ) ]
                { * | 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. By default, the new (post-update) values of the table's
   columns are used, but it is also possible to request the old
   (pre-update) values. 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 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). An
          identity column will be set to a new value generated by the
          associated sequence. For a generated column, specifying this is
          permitted but merely specifies the normal behavior of computing
          the column from its generation expression.

   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 for more
          information about using cursors with WHERE CURRENT OF.

   output_alias
          An optional substitute name for OLD or NEW rows in the RETURNING
          list.

          By default, old values from the target table can be returned by
          writing OLD.column_name or OLD.*, and new values can be returned
          by writing NEW.column_name or NEW.*. When an alias is provided,
          these names are hidden and the old or new rows must be referred
          to using the alias. For example RETURNING WITH (OLD AS o, NEW AS
          n) o.*, n.*.

   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.

          A column name or * may be qualified using OLD or NEW, or the
          corresponding output_alias for OLD or NEW, to cause old or new
          values to be returned. An unqualified column name, or *, or a
          column name or * qualified using the target table name or alias
          will return new values.

   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 of the containing partition. In
   that case, if there is some other partition in the partition tree for
   which this row satisfies its partition constraint, then the row is
   moved to that partition. If there is no such partition, an error will
   occur. Behind the scenes, the row movement is actually a DELETE and
   INSERT operation.

   There is a possibility that a concurrent UPDATE or DELETE on the row
   being moved will get a serialization failure error. Suppose session 1
   is performing an UPDATE on a partition key, and meanwhile a concurrent
   session 2 for which this row is visible performs an UPDATE or DELETE
   operation on this row. In such case, session 2's UPDATE or DELETE will
   detect the row movement and raise a serialization failure error (which
   always returns with an SQLSTATE code '40001'). Applications may wish to
   retry the transaction if this occurs. In the usual case where the table
   is not partitioned, or where there is no row movement, session 2 would
   have identified the newly updated row and carried out the UPDATE/DELETE
   on this new row version.

   Note that while rows can be moved from local partitions to a
   foreign-table partition (provided the foreign data wrapper supports
   tuple routing), they cannot be moved from a foreign-table partition to
   another partition.

   An attempt of moving a row from one partition to another will fail if a
   foreign key is found to directly reference an ancestor of the source
   partition that is not the same as the ancestor that's mentioned in the
   UPDATE query.

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, and the old
   precipitation value:
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, old.prcp AS old_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 salespeople:
UPDATE accounts SET (contact_first_name, contact_last_name) =
    (SELECT first_name, last_name FROM employees
     WHERE employees.id = accounts.sales_person);

   A similar result could be accomplished with a join:
UPDATE accounts SET contact_first_name = first_name,
                    contact_last_name = last_name
  FROM employees WHERE employees.id = accounts.sales_person;

   However, the second query may give unexpected results if employees.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_person 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;

   Updates affecting many rows can have negative effects on system
   performance, such as table bloat, increased replica lag, and increased
   lock contention. In such situations it can make sense to perform the
   operation in smaller batches, possibly with a VACUUM operation on the
   table between batches. While there is no LIMIT clause for UPDATE, it is
   possible to get a similar effect through the use of a Common Table
   Expression and a self-join. With the standard PostgreSQL table access
   method, a self-join on the system column ctid is very efficient:
WITH exceeded_max_retries AS (
  SELECT w.ctid FROM work_item AS w
    WHERE w.status = 'active' AND w.num_retries > 10
    ORDER BY w.retry_timestamp
    FOR UPDATE
    LIMIT 5000
)
UPDATE work_item SET status = 'failed'
  FROM exceeded_max_retries AS emr
  WHERE work_item.ctid = emr.ctid;

   This command will need to be repeated until no rows remain to be
   updated. Use of an ORDER BY clause allows the command to prioritize
   which rows will be updated; it can also prevent deadlock with other
   update operations if they use the same ordering. If lock contention is
   a concern, then SKIP LOCKED can be added to the CTE to prevent multiple
   commands from updating the same row. However, then a final UPDATE
   without SKIP LOCKED or LIMIT will be needed to ensure that no matching
   rows were overlooked.

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.