Some help with functions-syntax

I have some problem with writing a function.

I have made this function which I can't get it to work.

This is probaly a triviel question but i'm new to plsql, so this is a
showstopper for me.

DECLARE_relkind char;_RES "EMS"."KeySet";_WHERECLAUSE text;
BEGINSELECT pgc.relkind INTO _relkindFROM pg_class pgc JOIN pg_namespace pgn ON pgc.relnamespace=pgn.oidWHERE
pgn.nspname=$1AND pgc.relname=$2;
 
IF _relkind = 'r' THEN    _WHERECLAUSE := '(fknam.nspname = ''$1'' AND fkc.relname = ''$2'')';END IF;
IF _relkind = 'v' THEN    _WHERECLAUSE := '';END IF;
FOR _RES IN    SELECT    fknam.nspname AS "FKTABLE_SCHEM",        fkc.relname AS "FKTABLE_NAME",        fka.attname AS
"FKCOLUMN_NAME",       pknam.nspname AS "PKTABLE_SCHEM",        pkc.relname AS "PKTABLE_NAME",        pka.attname AS
"PKCOLUMN_NAME",       fkcon.conname AS "FK_NAME",        pkcon.conname AS "PK_NAME",        CASE            WHEN
pkcon.contype= 'p' THEN 'PRIMARY'            WHEN pkcon.contype = 'u' THEN 'UNIQUE'        END AS "UNIQUE_OR_PRIMARY"
FROM     pg_constraint AS fkcon        JOIN pg_namespace AS fknam ON fkcon.connamespace=fknam.oid        JOIN pg_class
ASfkc ON fkc.oid=fkcon.conrelid        JOIN pg_attribute fka ON fka.attrelid=fkc.oid AND fka.attnum =
 
ANY(fkcon.conkey)        JOIN pg_constraint AS pkcon ON fkcon.confrelid=pkcon.conrelid AND
fkcon.confkey=pkcon.conkey        JOIN pg_namespace pknam ON pkcon.connamespace=pknam.oid        JOIN pg_class pkc ON
pkc.oid=fkcon.confrelid       JOIN pg_attribute pka ON pka.attrelid=pkc.oid AND pka.attnum =
 
some(pkcon.conkey)    WHERE     (        (pkcon.conkey[1] = pka.attnum AND fkcon.conkey[1] = fka.attnum) OR
(pkcon.conkey[2]= pka.attnum AND fkcon.conkey[2] = fka.attnum) OR        (pkcon.conkey[3] = pka.attnum AND
fkcon.conkey[3]= fka.attnum) OR        (pkcon.conkey[4] = pka.attnum AND fkcon.conkey[4] = fka.attnum) OR
(pkcon.conkey[5]= pka.attnum AND fkcon.conkey[5] = fka.attnum)        ) AND || _WHERECLAUSE        LOOP    RETURN NEXT
_RES;ENDLOOP;RETURN;
 
END;

I get the following error:

ERROR: operator does not exist: || text
SQL state: 42883
Hint: No operator matches the given name and argument type(s). You may
need to add explicit type casts.


How do I solve this?

I also have a question about how to write CASE-statement? I am only able
to use if.

Regards

Jan