Transaction results in syntax error - postgresql

Question

This function is created ok without the transaction block. With it as in the following I get the following error...
ERROR: syntax error at end of input LINE 27: $$
^
********** Error **********
ERROR: syntax error at end of input
If I take out the 'COMMIT' and corresponding 'BEGIN' then it runs ok.
Why is this?
CREATE OR REPLACE FUNCTION ContentDelete (
creatorUserId BIGINT,
toDeleteContentId BIGINT)
RETURNS VOID
AS $$
BEGIN
BEGIN
IF (SELECT EXISTS(SELECT
*
FROM
tbl_content
WHERE
ContentId = toDeleteContentId
AND
UserId = creatorUserId
LIMIT 1) AS "exists")
THEN
DELETE FROM tbl_content WHERE ParentContentId = toDeleteContentId;
DELETE FROM tbl_content WHERE ContentId = toDeleteContentId;
END IF;
COMMIT;
END
$$
LANGUAGE plpgsql;

Answer 1

Functions in PostgreSQL are running under transaction everywhere. It can be implicit transaction (started by Postgres) or explicit transaction (started by user). And you cannot to commit or rollback this transaction, because it is started outside function.
If your function doesn't raise a exception, then result will be committed (if somebody else doesn't raise a exception). If you would to enforce rollback - raise a exception. The only one solution is rollback of outer transaction. Your function can be strongly reduced in PostgreSQL (although your logic looks messy):
CREATE OR REPLACE FUNCTION ContentDelete (creatorUserId BIGINT,
toDeleteContentId BIGINT)
RETURNS VOID AS $$
BEGIN
DELETE FROM tbl_content
WHERE ContentId = toDeleteContentId
AND UserId = creatorUserId;
IF FOUND THEN
DELETE FROM tbl_content WHERE ParentContentId = toDeleteContentId;
END IF;
RETURN;
END;
$$ LANGUAGE plpgsql;