Postgresql – nyway to UPDATE a series of columns on a row with a composite type record/row

composite-typespostgresqlpostgresql-9.5rowupdate

Take a table foo,

CREATE TABLE foo(a,b,c,d)
AS VALUES
  (1,2,3,4);

I can insert into foo with a row type..

INSERT INTO foo
  SELECT (foo).*
  FROM foo;

INSERT INTO foo
  SELECT (v).*
  FROM ( VALUES (42,42,42,42) )
    AS v;

But I can't update foo with a row type.

-- fails
UPDATE foo SET (a,b,c,d) = (
  SELECT ROW(1,2,3,4)
).*;

-- also fails.
UPDATE foo SET (a,b,c,d) = (SELECT (1,2,3,4));
ERROR:  number of columns does not match number of values
LINE 1: UPDATE foo SET (a,b,c,d) = (SELECT (1,2,3,4));

Is there any syntax to update an entire row with a composite type. The really weird thing is that this works in a trigger with NEW, and I'm trying to write the same code without a trigger.

CREATE OR REPLACE FUNCTION foo()
RETURNS trigger
AS $$
  BEGIN
    NEW=(42,42,42,42);
    RETURN NEW;
  END;
$$ LANGUAGE plpgsql
IMMUTABLE;

CREATE TRIGGER ok
  BEFORE UPDATE ON foo
  FOR EACH ROW
  EXECUTE PROCEDURE foo();

-- The NEW row in trigger gets updated with (42,42,42,42)
-- the UPDATE succeeds; all rows (42,42,42,42)
UPDATE foo
  SET (a,b,c,d) = (1,2,3,4);

You can see here that we can update the row object inside the procedure, and change the update. However, we can't do that in the UPDATE ddl? I would expect the RECORD produced by the same name of the table to work the same way.

-- Such as this,
UPDATE foo
  SET foo = (1,2,3,4);

Best Answer

There are actually lots of posts regarding this..

However, according to /u/pstef, one of these is committed, and this syntax now works on HEAD, though @ypercubeᵀᴹ reports it does not work on 9.6.5

UPDATE foo SET (a,b,c,d) = ROW(10,9,8,7);

The docs don't say much about this

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.

But you can also see at the syntax for UPDATE

   ( column_name [, ...] ) = [ ROW ] ( { expression | DEFAULT } [, ...] ) |
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