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PostgreSQL Reference Manual - Volume 2 - Programming Guide
by The PostgreSQL Global Development Group
Paperback (6"x9"), 408 pages
ISBN 0954612035
RRP £19.95 ($34.95)

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5.4.5 SQL Functions Returning Sets

When an SQL function is declared as returning SETOF sometype, the function's final SELECT query is executed to completion, and each row it outputs is returned as an element of the result set.

This feature is normally used when calling the function in the FROM clause. In this case each row returned by the function becomes a row of the table seen by the query. For example, assume that table foo has the same contents as above, and we say:

    SELECT * FROM foo WHERE fooid = $1;

SELECT * FROM getfoo(1) AS t1;

Then we would get:

 fooid | foosubid | fooname
     1 |        1 | Joe
     1 |        2 | Ed
(2 rows)

Currently, functions returning sets may also be called in the select list of a query. For each row that the query generates by itself, the function returning set is invoked, and an output row is generated for each element of the function's result set. Note, however, that this capability is deprecated and may be removed in future releases. The following is an example function returning a set from the select list:

CREATE FUNCTION listchildren(text) RETURNS SETOF text AS $$
    SELECT name FROM nodes WHERE parent = $1

SELECT * FROM nodes;
   name    | parent
 Top       |
 Child1    | Top
 Child2    | Top
 Child3    | Top
 SubChild1 | Child1
 SubChild2 | Child1
(6 rows)

SELECT listchildren('Top');
(3 rows)

SELECT name, listchildren(name) FROM nodes;
  name  | listchildren
 Top    | Child1
 Top    | Child2
 Top    | Child3
 Child1 | SubChild1
 Child1 | SubChild2
(5 rows)

In the last SELECT, notice that no output row appears for Child2, Child3, etc. This happens because listchildren returns an empty set for those arguments, so no result rows are generated.

ISBN 0954612035PostgreSQL Reference Manual - Volume 2 - Programming GuideSee the print edition