Declaring the tuple structure of a record in PL/pgSQL

I can't find anything in the PostgreSQL documentation that shows how to declare a record, or row, while declaring the tuple structure at the same time. If you don't define you tuple structure you get the error "The tuple structure of a not-yet-assigned record is indeterminate".

This is what I'm doing now, which works fine, but there must be a better way to do it.

CREATE OR REPLACE FUNCTION my_func()
  RETURNS TABLE (
    "a" integer,
    "b" varchar
  ) AS $$
DECLARE r record;
BEGIN

CREATE TEMP TABLE tmp_t (
    "a" integer,
    "b" varchar
);
-- Define the tuple structure of r by SELECTing an empty row into it.
-- Is there a more straight-forward way of doing this?
SELECT * INTO r
FROM tmp_t;

-- Now I can assign values to the record.
r.a := at.something FROM "another_table" at
       WHERE at.some_id = 1;

-- A related question is - how do I return the single record 'r' from
-- this function?
-- This works:
RETURN QUERY
SELECT * FROM tmp_t;

-- But this doesn't:
RETURN r;
-- ERROR:  RETURN cannot have a parameter in function returning set

END; $$ LANGUAGE plpgsql;

Erwin Brandstetter

You are mixing the syntax for returning SETOF values with syntax for returning a single row or value.

-- A related question is - how do I return the single record 'r' from

When you declare a function with RETURNS TABLE, you have to use RETURN NEXT in the body to return a row (or scalar value). And if you want to use a record variable with that it has to match the return type. Refer to the code examples further down.

Return a single value or row

If you just want to return a single row, there is no need for a record of undefined type. @Kevin already demonstrated two ways. I'll add a simplified version with OUT parameters:

CREATE OR REPLACE FUNCTION my_func(OUT a integer, OUT b text)
   AS
$func$
BEGIN
   a := ...;
   b := ...;
END
$func$ LANGUAGE plpgsql;

You don't even need to add RETURN; in the function body, the value of the declared OUT parameters will be returned automatically at the end of the function - NULL for any parameter that has not been assigned.
And you don't need to declare RETURNS RECORD because that's already clear from the OUT parameters.

Return a set of rows

If you actually want to return multiple rows (including the possibility for 0 or 1 row), you can define the return type as RETURNS ...

SETOF some_type, where some_type can be any registered scalar or composite type.
TABLE (col1 type1, col2 type2) - an ad-hoc row type definition.
SETOF record plus OUT parameters to define column names andtypes.
100% equivalent to RETURNS TABLE.
SETOF record without further definition. But then the returned rows are undefined and you need to include a column definition list with every call (see example).

The manual about the record type:

Record variables are similar to row-type variables, but they have no predefined structure. They take on the actual row structure of the row they are assigned during a SELECT or FOR command.

There is more, read the manual.

You can use a record variable without assigning a defined type, you can even return such undefined records:

CREATE OR REPLACE FUNCTION my_func()
  RETURNS SETOF record AS
$func$
DECLARE
    r record;
BEGIN
    r := (1::int, 'foo'::text); RETURN NEXT r; -- works with undefined record
    r := (2::int, 'bar'::text); RETURN NEXT r;
END
$func$ LANGUAGE plpgsql;

Call:

SELECT * FROM my_func() AS x(a int, b text);

But this is very unwieldy as you have to provide the column definition list with every call. It can generally be replaced with something more elegant:

If you know the type at time of function creation, declare it right away (RETURNS TABLE or friends).

CREATE OR REPLACE FUNCTION my_func()
  RETURNS SETOF tbl_or_type AS
$func$
DECLARE
    r tbl_or_type;
BEGIN
    SELECT INTO tbl_or_type  * FROM tbl WHERE id = 10;
    RETURN NEXT r;  -- type matches

    SELECT INTO tbl_or_type  * FROM tbl WHERE id = 12;
    RETURN NEXT r;

    -- Or simpler:
    RETURN QUERY
    SELECT * FROM tbl WHERE id = 14;
END
$func$ LANGUAGE plpgsql;

If you know the type at time of the function call, there are more elegant ways using polymorphic types:
Refactor a PL/pgSQL function to return the output of various SELECT queries

Your question is unclear as to what you need exactly.

There might be some way that avoids the explicit type declaration, but offhand the best I can come up with is:

CREATE TYPE my_func_return AS (
    a integer,
    b varchar
  );

CREATE OR REPLACE FUNCTION my_func()
  RETURNS my_func_return AS $$
DECLARE
  r my_func_return;
BEGIN
  SELECT 1, 'one' INTO r.a, r.b;
  RETURN r;
END; $$ LANGUAGE plpgsql;

Oh, I almost forgot the simplest way to do this:

CREATE OR REPLACE FUNCTION my_func2(out a int, out b text)
  RETURNS RECORD AS $$
BEGIN
  SELECT 1, 'one' INTO a, b;
  RETURN;
END; $$ LANGUAGE plpgsql;

Craig Ringer

It is much easier to use OUT parameters rather than a record. If iteratively building a set of records (a table) use RETURN NEXT. If generating from a query, use RETURN QUERY. See:

https://stackoverflow.com/a/955289/398670

and:

http://www.postgresql.org/docs/current/static/plpgsql-declarations.html http://www.postgresql.org/docs/current/static/sql-createfunction.html http://www.postgresonline.com/journal/archives/129-Use-of-OUT-and-INOUT-Parameters.html

Think:

CREATE OR REPLACE FUNCTION my_func(OUT a integer, OUT b varchar) RETURNS SETOF RECORD AS $$
BEGIN
    -- Assign a and b, RETURN NEXT, repeat. when done, RETURN.
END;
$$ LANGUAGE 'plpgsql';

来源：https://stackoverflow.com/questions/11907563/declaring-the-tuple-structure-of-a-record-in-pl-pgsql

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