Oracle SQL reference outer table field in derived table nested query - sql

Question

I need to reference a field from the outer query in a derived table . The issue is that I need to limit the max date that is fetched from the derived table using a value from the outer table (A in this case) because the outer table is a temp work table that is populated with specific values by a process.
Below approach is incorrect as it cannot reference the outer table correctly. Is there a better way to write this?
Below is the example of how I want it to work:
SELECT A.EMP, X.SCHEDULE, A.DATE FROM CUST A, (SELECT T1.EMP, T1.NAME, CASE WHEN T1.USER1 = '3' THEN T2.USER4 ELSE T1.USER4 END AS Schedule
FROM TEMP1 T1, TEMP2 T2, TEMP3 T3
WHERE T1.EMP = T3.EMP
AND T2.VALUE= T3.VALUE
AND T1.DATE = (SELECT MAX(T1A.DATE) FROM TEMP1 T1A
WHERE T1A.EMP = T1.EMP
AND T1A.DATE <= A.DATE)
AND T2.DATE = (SELECT MAX(T2A.DATE) FROM TEMP2 T2A
WHERE T2A.VALUE= T2.VALUE
AND T2A.DATE <= A.DATE)
AND T3.DATE = (SELECT MAX(T3A.DATE) FROM TEMP3 T3A
WHERE T3A.EMP = T3.EMP
AND T3A.VALUE = T3.VALUE
AND T3A.DATE <= A.DATE)) X
WHERE A.EMP = X.EMP
AND X.EMP IN ('1','2');
Below is some sample data and results:
TABLE CUST
EMP DATE VALUE
1 1/1/17 R
2 2/1/17 R
TABLE TEMP1
EMP DATE USER1 USER4
1 3/2/16 3 4
1 5/1/17 3 3
2 2/1/17 9 2
TABLE TEMP2
DATE VALUE USER4
1/1/01 S 100
1/1/03 P 200
1/3/07 R 300
8/1/17 R 350
TABLE TEMP3
EMP DATE VALUE
1 3/2/16 R
1 5/1/17 R
2 2/1/17 R
The sample output should be:
EMP SCHEDULE DATE
1 300 1/1/17
2 2 2/1/17

Answer 1

I tried with your sample data and i got the output. I have rewritten your query and got the output expected.
SELECT A.emp, A.tdate,
CASE WHEN T1.USER1 = '3' THEN T2.USER4 ELSE T1.USER4 END AS Schedule
FROM CUST A, Temp1 t1, temp2 t2, temp3 t3
WHERE A.emp=t1.emp
AND A.tvalue = t2.tvalue
AND A.emp = t3.emp
AND A.tvalue = t3.tvalue
AND t1.tdate <=(SELECT max(tdate) from temp1 t where tdate<=A.tdate and t.emp=A.emp)
AND t2.tdate <= (SELECT max(tdate) from temp2 t where tdate <= A.tdate and A.tvalue = t.tvalue)
AND t3.tdate <=(SELECT max(tdate) from temp3 t where tdate <= A.tdate and A.tvalue = t.tvalue and t.emp=A.emp)
If you are going to have only one date in temp tables that is less than the date in cust table, then use the below query
SELECT A.emp, A.tdate,
CASE WHEN T1.USER1 = '3' THEN T2.USER4 ELSE T1.USER4 END AS Schedule
FROM CUST A, Temp1 t1, temp2 t2, temp3 t3
WHERE A.emp=t1.emp
AND A.tvalue = t2.tvalue
AND A.emp = t3.emp
AND A.tvalue = t3.tvalue
AND t1.tdate <=A.tdate
AND t2.tdate <= A.tdate
AND t3.tdate <= A.tdate
NOTE:- Column names like date and value willl throw error while table creation. They are reserved keywords

Answer 2

As "date" is a SQL reserved word (for a data type in Oracle) I would never use that as a column name. Below I have used DATECOL instead.
I think it is much easier to just compare the dates via a simple set of joins.
See this working here at SQL Fiddle
CREATE TABLE CUST
(EMP int, DATECOL date, VALUE varchar2(1))
;
INSERT ALL
INTO CUST (EMP, DATECOL, VALUE)
VALUES (1, to_date('01-Jan-2017','dd-mon-yyyy'), 'R')
INTO CUST (EMP, DATECOL, VALUE)
VALUES (2, to_date('01-Feb-2017','dd-mon-yyyy'), 'R')
SELECT * FROM dual
;
CREATE TABLE TEMP1
(EMP int, DATECOL date, USER1 int, USER4 int)
;
INSERT ALL
INTO TEMP1 (EMP, DATECOL, USER1, USER4)
VALUES (1, to_date('02-Mar-2016','dd-mon-yyyy'), 3, 4)
INTO TEMP1 (EMP, DATECOL, USER1, USER4)
VALUES (1, to_date('01-May-2017','dd-mon-yyyy'), 3, 3)
INTO TEMP1 (EMP, DATECOL, USER1, USER4)
VALUES (2, to_date('01-Feb-2017','dd-mon-yyyy'), 9, 2)
SELECT * FROM dual
;
CREATE TABLE TEMP2
(DATECOL date, VALUE varchar2(1), USER4 int)
;
INSERT ALL
INTO TEMP2 (DATECOL, VALUE, USER4)
VALUES (to_date('01-Jan-2001','dd-mon-yyyy'), 'S', 100)
INTO TEMP2 (DATECOL, VALUE, USER4)
VALUES (to_date('01-Jan-2003','dd-mon-yyyy'), 'P', 200)
INTO TEMP2 (DATECOL, VALUE, USER4)
VALUES (to_date('03-Jan-2007','dd-mon-yyyy'), 'R', 300)
INTO TEMP2 (DATECOL, VALUE, USER4)
VALUES (to_date('01-Aug-2017','dd-mon-yyyy'), 'R', 350)
SELECT * FROM dual
;
CREATE TABLE TEMP3
(EMP int, DATECOL date, VALUE varchar2(1))
;
INSERT ALL
INTO TEMP3 (EMP, DATECOL, VALUE)
VALUES (1, to_date('02-Mar-2016','dd-mon-yyyy'), 'R')
INTO TEMP3 (EMP, DATECOL, VALUE)
VALUES (1, to_date('01-May-2017','dd-mon-yyyy'), 'R')
INTO TEMP3 (EMP, DATECOL, VALUE)
VALUES (2, to_date('01-Feb-2017','dd-mon-yyyy'), 'R')
SELECT * FROM dual
;
Query 1:
SELECT
T1.EMP
--, T1.NAME
, CASE WHEN T1.USER1 = '3'
THEN
T2.USER4 ELSE
T1.USER4
END AS Schedule
, c.datecol
, t1.datecol t1date
, t2.datecol t2date
, t3.datecol t3date
FROM TEMP1 T1
INNER JOIN cust c ON T1.EMP = c.EMP
INNER JOIN TEMP3 T3 ON T1.EMP = T3.EMP
INNER JOIN TEMP2 T2 ON T3.VALUE = T2.VALUE
WHERE t1.datecol <= c.datecol
AND t2.datecol <= c.datecol
AND t3.datecol <= c.datecol
Results:
| EMP | SCHEDULE | DATECOL | T1DATE | T2DATE | T3DATE |
|-----|----------|----------------------|----------------------|----------------------|----------------------|
| 1 | 300 | 2017-01-01T00:00:00Z | 2016-03-02T00:00:00Z | 2007-01-03T00:00:00Z | 2016-03-02T00:00:00Z |
| 2 | 2 | 2017-02-01T00:00:00Z | 2017-02-01T00:00:00Z | 2007-01-03T00:00:00Z | 2017-02-01T00:00:00Z |
Also, over 25 years ago SQL standardized on a way better method of joining tables together. This simple trick to remember is stop using commas between table names in the FROM clause. This helps to ensure explicit join syntax is adopted.