SQL function return-type: TABLE vs SETOF records

问题

What's the difference between a function that returns TABLE vs SETOF records, all else equal.

CREATE FUNCTION events_by_type_1(text) RETURNS TABLE(id bigint, name text) AS $$
    SELECT id, name FROM events WHERE type = $1;
$$ LANGUAGE SQL STABLE;

CREATE FUNCTION events_by_type_2(text) RETURNS SETOF record AS $$
    SELECT id, name FROM events WHERE type = $1;
$$ LANGUAGE SQL STABLE;

These functions seem to return the same results. See this SQLFiddle.

回答1:

When returning SETOF record the output columns are not typed and not named. Thus this form can't be used directly in a FROM clause as if it was a subquery or a table.

That is, when issuing:

SELECT * from events_by_type_2('social');

we get this error:

ERROR: a column definition list is required for functions returning "record"

It can be "casted" into the correct column types by the SQL caller though. This form does work:

SELECT * from events_by_type_2('social') as (id bigint, name text);

and results in:

 id |      name      
----+----------------
  1 | Dance Party
  2 | Happy Hour
 ...

For this reason SETOF record is considered less practical. It should be used only when the column types of the results are not known in advance.

回答2:

This answer is only to remember alternative context where TABLE and SETOF are equivalent.

As @a_horse_with_no_name pointed, it is not a RETURNS SETOF "unknown record", is a defined one.

In this example, the types table and setof are equivalent,

CREATE TYPE footype AS (score int, term text);

CREATE FUNCTION foo() RETURNS SETOF footype AS $$
   SELECT * FROM ( VALUES (1,'hello!'), (2,'Bye') ) t;
$$ language SQL immutable;

CREATE FUNCTION foo_tab() RETURNS TABLE (score int, term text) AS $$
   SELECT * FROM ( VALUES (1,'hello!'), (2,'Bye') ) t;
$$ language SQL immutable;

SELECT * FROM foo();      -- works fine!
SELECT * FROM foo_tab();  -- works fine and is equivalent.

The RETURNS SETOF have the advantage of reuse type (see footype), that is impossible with RETURNS TABLE.

来源：https://stackoverflow.com/questions/22423958/sql-function-return-type-table-vs-setof-records

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sql

postgresql

return-type

sql-function

sql-types