Syntax error on postgresql function. impossible syntax - postgresql

Question

I try to correct this function but is impossible!!
I declare one integer "var_id", and insert in id_val the value of frist query,
if is null the tag name is inserted in a table and var_id = last insert id, otherwise do the last insert...
CREATE OR REPLACE FUNCTION public."InsertVideoTag"
(
IN in_idvideo integer,
IN in_tagname VARCHAR(25)
)
RETURNS bigint AS
$$
DECLARE var_id bigint DEFAULT NULL;
SELECT var_id := IDTag FROM Tag WHERE TagName = in_tagname;
IF var_id IS NULL
THEN
INSERT INTO tag ( TagName )
VALUES( in_tagname );
var_id := SELECT CURRVAL(pg_get_serial_sequence('public.tag','idtag'));
END IF;
INSERT INTO video_has_tag
(
IDVideo,
IDTag
)
VALUES
(
in_idvideo,
var_id
);
SELECT CURRVAL(pg_get_serial_sequence('public.video','idvideo'));
$$
LANGUAGE 'plpgsql'
VOLATILE
CALLED ON NULL INPUT
SECURITY INVOKER;

Answer 1

The function can be converted into a pure SQL one, which will make it much better performing one. Also I've noted, that the current functionality will create duplicate entries in the video_has_tag table if called multiple times with the same arguments.
I've changed the function to be idempotent.
First table structure that I've assumed:
CREATE TABLE tag (
idTag serial,
tagName text);
CREATE TABLE video_has_tag (
idVideo integer,
idTag integer);
And then the function itself:
CREATE OR REPLACE FUNCTION insVideoTag(in_idvideo integer, in_tagname text)
RETURNS integer STRICT AS $insVideoTag$
WITH
new_tag AS (
INSERT INTO tag (tagName)
SELECT $2
WHERE NOT EXISTS (SELECT 1 FROM tag WHERE tagName = $2)
RETURNING idTag, tagName
), tag_data AS (
SELECT * FROM new_tag
UNION
SELECT idTag, tagName FROM tag
WHERE tagName = $2
), new_target AS (
INSERT INTO video_has_tag(idVideo, idTag)
SELECT $1, td.idTag
FROM tag_data td
WHERE NOT EXISTS (SELECT 1 FROM video_has_tag
WHERE idVideo=$1 AND idTag=td.idTag)
RETURNING idVideo, idTag
)
SELECT idVideo FROM (
SELECT * FROM new_target
UNION
SELECT * FROM video_has_tag
WHERE idVideo=$1 AND idTag=(SELECT idTag FROM tag_data)
) s;
$insVideoTag$ LANGUAGE sql;

Answer 2

No need for if statements, a where clause is enough:
selecting the current value is not suitable as a return value (or to be entered into an other tables FK) : it could have been bumped after the first insert.
DROP SCHEMA tmp CASCADE;
CREATE SCHEMA tmp ;
SET search_path=tmp;
CREATE TABLE tag
( idtag SERIAL NOT NULL PRIMARY KEY
, tagname varchar
);
CREATE TABLE video_has_tag
( idvideo INTEGER NOT NULL
, idtag INTEGER NOT NULL REFERENCES tag (idtag)
);
CREATE OR REPLACE FUNCTION tmp.insertvideotag
( in_idvideo integer , in_tagname VARCHAR )
RETURNS bigint AS
$$
DECLARE var_id bigint DEFAULT NULL;
BEGIN
INSERT INTO tag (tagname )
SELECT in_tagname
WHERE NOT EXISTS (
SELECT * FROM tag
WHERE tagname = in_tagname
);
INSERT INTO video_has_tag (idvideo,idtag)
SELECT in_idvideo, tg.idtag
FROM tag tg
WHERE tg.tagname = in_tagname
RETURNING idtag
INTO var_id
;
RETURN var_id;
END;
$$
LANGUAGE 'plpgsql'
VOLATILE
CALLED ON NULL INPUT
SECURITY INVOKER;
SELECT insertvideotag(11, 'Eleven');
SELECT insertvideotag(12, 'Eleven');
SELECT insertvideotag(13, 'Thirteen');
SELECT tv.idvideo
,tv.idtag, tg.tagname
FROM video_has_tag tv
JOIN tag tg ON tg.idtag = tv.idtag
;
Result:
NOTICE: CREATE TABLE will create implicit sequence "tag_idtag_seq" for serial column "tag.idtag"
NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "tag_pkey" for table "tag"
CREATE TABLE
CREATE TABLE
CREATE FUNCTION
insertvideotag
----------------
1
(1 row)
insertvideotag
----------------
2
(1 row)
idvideo | idtag | tagname
---------+-------+----------
11 | 1 | Eleven
12 | 1 | Eleven
13 | 2 | Thirteen
(2 rows)

Answer 3

CREATE OR REPLACE FUNCTION public."InsertVideoTag"
(
IN in_idvideo integer,
IN in_tagname VARCHAR(25)
)
RETURNS bigint AS
$$
DECLARE var_id bigint DEFAULT NULL;
begin
var_id := (select IDTag FROM Tag WHERE TagName = in_tagname);
IF var_id IS NULL
THEN
INSERT INTO tag ( TagName )
VALUES( in_tagname );
var_id := (SELECT CURRVAL(pg_get_serial_sequence('public.tag','idtag')));
END IF;
INSERT INTO video_has_tag
(
IDVideo,
IDTag
)
VALUES
(
in_idvideo,
var_id
);
return (SELECT CURRVAL(pg_get_serial_sequence('public.video','idvideo')));
end;
$$
LANGUAGE 'plpgsql'
VOLATILE
CALLED ON NULL INPUT
SECURITY INVOKER;

Answer 4

I've found it's much easier to work with lower case columns & table names, etc. with postgres, so I've made a few changes to your existing code :
CREATE OR REPLACE FUNCTION public."insertvideotag"
(
IN in_idvideo integer,
IN in_tagname VARCHAR(25)
)
RETURNS bigint AS
$$
DECLARE var_id bigint DEFAULT NULL;
BEGIN
--SELECT var_id := IDTag FROM Tag WHERE TagName = in_tagname;
SELECT idtag into var_id FROM tag WHERE tagname = in_tagname;
IF var_id IS NULL
THEN
INSERT INTO tag ( TagName )
VALUES( in_tagname );
--var_id := SELECT CURRVAL(pg_get_serial_sequence('public.tag','idtag'));
SELECT CURRVAL(pg_get_serial_sequence('public.tag','idtag')) into var_id;
END IF;
INSERT INTO video_has_tag
(
idvideo,
idtag
)
VALUES
(
in_idvideo,
var_id
);
SELECT CURRVAL(pg_get_serial_sequence('public.video','idvideo'));
END
$$
LANGUAGE 'plpgsql'
VOLATILE
CALLED ON NULL INPUT
SECURITY INVOKER;
The remaining potential issues are the sequence names, and perhaps what value you'd like to return.