Dynamic column name with SELECT INTO

Question

I am trying to build a function that derives a pay amount from a set of business rules. There are about 40 columns that hold various pay amounts and their column names are variations of 4 indicators (day shift, vs night shift, etc.) that I have to dynamically look up, ie here is the ID number and a timecard, now figure out which of the 40 fields to look up to get the pay amount.
I can determine from the timecard and employee ID which field to look at, but I'm getting hung up with the syntax needed to construct and execute the statement inside the PL/SQL block. I need to RETURN the pay I extract using the function, and I can create the correct SQL statement, but the EXECUTE IMMEDIATE won't accept the SELECT INTO syntax.
Can someone please suggest a solution? Here is the function:
create or replace FUNCTION FN_GET_PAYRATE(tc in NUMBER, e in NUMBER, pc in VARCHAR2)
RETURN NUMBER
IS
e_id NUMBER;
tc_id NUMBER;
pl_cd VARCHAR2(7);
shft VARCHAR2(2);
lvl VARCHAR2(2);
typ VARCHAR2(2);
e_typ VARCHAR2(4);
proj NUMBER;
hrly VARCHAR2(4);
payrt NUMBER;
var_col VARCHAR2(10);
sql_select VARCHAR2(200);
sql_from VARCHAR2(200);
sql_where VARCHAR2(200);
sql_and1 VARCHAR2(200);
sql_and2 VARCHAR2(200);
sql_and3 VARCHAR2(200);
sql_orderby VARCHAR2(200);
var_sql VARCHAR2(2000);
BEGIN
e_id := e;
tc_id := tc;
pl_cd := pc;
SELECT NVL(SHIFT,'D') INTO shft
FROM TS_TIMECARD_MAIN
WHERE TIMECARD_ID = tc_id;
--DBMS_OUTPUT.PUT_LINE('SHIFT= ' || shft);
SELECT NVL(PAY_LVL, 1), NVL(PAY_TYPE, 'B'), NVL(RTRIM(EMP_TYPE), 'LHD'), NVL(PROJECT, 001)
INTO lvl, typ, e_typ, proj
FROM TS_EMPLOYEES
WHERE EMP_ID = e_id;
--DBMS_OUTPUT.PUT_LINE('Level= ' || lvl);
--DBMS_OUTPUT.PUT_LINE('PAY_TYPE= ' || typ);
--DBMS_OUTPUT.PUT_LINE('EMP_TYPE= ' || e_typ);
--DBMS_OUTPUT.PUT_LINE('PROJECT= ' || proj);
IF e_typ <> 'LHD' THEN
hrly := 'H';
ELSE
hrly := '';
END IF;
IF proj <> 001 THEN
var_col := shft || lvl || typ || hrly;
--DBMS_OUTPUT.PUT_LINE('RATE COLUMN= ' || var_col);
sql_select := 'SELECT NVL(' || var_col || ', .01) INTO payrt';
sql_from := ' FROM TS_PAYRATES';
sql_where := ' WHERE PROJECT_ID = ' || proj;
sql_and1 := ' AND ACTIVE = 1';
sql_and2 := ' AND JOB_TYPE = ' || CHR(39) || e_typ || CHR(39);
sql_and3 := ' AND PILE_ID = ' || CHR(39) || pl_cd || CHR(39);
var_sql := sql_select || sql_from || sql_where || sql_and1 || sql_and2 || sql_and3 || sql_orderby;
DBMS_OUTPUT.PUT_LINE('SQL: ' || var_sql);
EXECUTE IMMEDIATE var_sql;
DBMS_OUTPUT.PUT_LINE('RATE= ' || payrt);
RETURN payrt;
ELSE
DBMS_OUTPUT.PUT_LINE('ERROR');
RETURN 1;
END IF;
END;
I have alternately tried this:
SELECT NVL(var_col,.01) into payrt
FROM TS_PAYRATES
WHERE PROJECT_ID = proj AND ACTIVE = 1
AND JOB_TYPE = CHR(39) || e_typ || CHR(39)
AND PILE_ID = CHR(39) || pl_cd || CHR(39);
as a substitute for the EXECUTE IMMEDIATE block, but I can't seem to use a dynamic substitution for the column name.
Any help would be greatly appreciated.

Answer 1

That's the most difficult part - the error messages seem to indicate a problem with the SQL statement in its execution context, because I can take the SQL string by itself and it executes perfectly.
Here are three variations:
SELECT INTO
select fn_get_payrate(21555, 30162, 15) from dual
ERROR at line 1:
ORA-00905: missing keyword
ORA-06512: at "PEOPLENETIF.FN_GET_PAYRATE", line 60
SQL: SELECT NVL(N4P , .01) INTO payrt FROM TS_PAYRATES WHERE PROJECT_ID = 701 AND ACTIVE = 1 AND JOB_TYPE = 'LHD' AND PILE_ID = '15'
Without SELECT INTO  (returns NULL)
SQL> select fn_get_payrate(21555, 30162, 15) from dual;
FN_GET_PAYRATE(21555,30162,15)
SQL: SELECT NVL(N4P , .01) FROM TS_PAYRATES WHERE PROJECT_ID = 701 AND ACTIVE = 1 AND JOB_TYPE = 'LHD' AND PILE_ID = '15'
RATE=
EXECUTE IMMEDIATE USING
SQL> select fn_get_payrate(21555, 30162, 15) from dual;
select fn_get_payrate(21555, 30162, 15) from dual
ERROR at line 1:
ORA-01006: bind variable does not exist
ORA-06512: at "PEOPLENETIF.FN_GET_PAYRATE", line 61
SQL: SELECT NVL(N4P , .01) FROM TS_PAYRATES WHERE PROJECT_ID = 701 AND ACTIVE = 1 AND JOB_TYPE = 'LHD' AND PILE_ID = '15'