conditional joining in oracle - sql

Question

Conditional joining statement : -
High level Description :-
Join table based on two columns if combination is not present then join on one table -
Detailed Table -
create table tab1
(tab1_col1 number not null,
tab1_col2 number null,
tab1_col3 varchar(10));
Lookup Table
create table lkp1
(lkp_col1 number not null,
lkp_col2 number not null,
lkp_col3 number not null,
lkp_col4 varchar(10));
Insert Statement -
tab1
insert into tab1 values (10,101,'A');
insert into tab1 values (12,101,'B');
insert into tab1 values (11,102,'C');
insert into tab1 values (13,103,'B');
insert into tab1 values (14,104,'C');
insert into tab1 values (15,108,'A');
insert into tab1 values (16,102,'D');
Lookup Table
lkp1
insert into lkp1 values (10,101,50,'PICK');
insert into lkp1 values (10,101,50,'PICK');
insert into lkp1 values (11,102,100,'SKIP');
insert into lkp1 values (11,110,50,'PICK');
insert into lkp1 values (13,103,40,'PICK');
insert into lkp1 values (13,103,60,'PICK');
insert into lkp1 values (14,199,100,'PICK');
insert into lkp1 values (15,115,80,'PICK');
insert into lkp1 values (15,115,20,'PICK');
Requirement was -
Join table based on tab1_col1=lkp_col1
and
tab1_col2=lkp_col2
Filter out lookup table data lkp_col4=SKIP
If record not present in lookup table for then give default value(99.99).
(All records from tab1 table should be selected).
I built this query and it was working fine.
SELECT tab1_col1, tab1_col2, NVL (lkp_col3, '99.99') "LKP_COL3"
FROM tab1,
(SELECT *
FROM lkp1
WHERE lkp_col4 = 'PICK') lkp
WHERE tab1_col1 = lkp_col1(+) AND tab1_col2 = lkp_col2(+)
Now requirement changed
First check if
tab1_col1=lkp_col1
and
tab1_col2=lkp_col2
If lookup table is not having data for this combination
then check again with
tab1_col1=lkp_col1
If this is not also available then give dafault value.
Database - Oracle 10g
What I have tried so far
After lot of trail and error I m able to get the output. However, is there a better or simple way to use this ?
SELECT tab1_col1, tab1_col2, LKP_COL3
FROM tab1,
(SELECT *
FROM lkp1
WHERE lkp_col4 = 'PICK') lkp
WHERE tab1_col1 = lkp_col1 AND tab1_col2 = lkp_col2
union all
SELECT tab1_col1, tab1_col2, LKP_COL3
FROM tab1,
(SELECT *
FROM lkp1
WHERE lkp_col4 = 'PICK') lkp
WHERE tab1_col1 = lkp_col1(+)
AND
LKP_COL1|| '-' || LKP_COL2 not in( SELECT tab1_col1|| '-' || tab1_col2
FROM tab1, lkp1 lkp
WHERE tab1_col1 = lkp_col1 AND tab1_col2 = lkp_col2)
order by 1

Answer 1

The following result:
| TAB1_COL1 | TAB1_COL2 | LKP_COL3 |
|-----------|-----------|----------|
| 10 | 101 | 50 |
| 11 | 102 | 50 |
| 12 | 101 | 99.99 |
| 13 | 103 | 40 |
| 13 | 103 | 60 |
| 14 | 104 | 100 |
| 15 | 108 | 20 |
| 15 | 108 | 80 |
| 16 | 102 | 99.99 |
was produced by this query:
SELECT DISTINCT
tab1.tab1_col1
, tab1.tab1_col2
, COALESCE(lkp1.lkp_col3, lkp2.lkp_col3, 99.99) "LKP_COL3"
FROM tab1
LEFT JOIN lkp1
ON tab1.tab1_col1 = lkp1.lkp_col1
AND tab1.tab1_col2 = lkp1.lkp_col2
AND lkp1.lkp_col4 = 'PICK'
LEFT JOIN lkp1 lkp2
ON tab1.tab1_col1 = lkp2.lkp_col1
AND lkp2.lkp_col4 = 'PICK'
ORDER BY
tab1.tab1_col1
, tab1.tab1_col2
;
DISTINCT was added because the second left (outer) join produces unwanted repetition in the output.
refer to this sqlfiddle