Using Decode Or Case Statement / Any Method

Question

Dear All,
In my table Fields are
EmpId
TranYear
TranMonth
ApprovedBy
ApprovedYear
ApprovedMonth
My Input parameters are
1. TranYear
2. TranMonth
3. Tag1
4. Tag2
My requirement is
Tag1 Input are 0,1,2
Tag2 Inputs are 0,1,2
If Tag1 is 0 then checking TranYear/TranMonth And
Tag2 Is 0 Then ApprovedBy Is Not Null only
Tag2 Is 1 Then ApprovedBy Is Null only
Tag2 Is 2 Then both(Approved/unApproved)
If Tag1 is 1 then checking ApprovedYear/ApprovedMonth And Tag2 Passing 0 Default
If Tag1 is 2 then checking TranYear/TranMonth Or ApprovedYear/ApprovedMonth And
Tag2 Is 0 Then ApprovedBy Is Not Null only
Tag2 Is 1 Then ApprovedBy Is Null only
Tag2 Is 2 Then both(Approved/unApproved)
Based upon the input details select details

Answer 1

dont quite understand your table structure requirement but it sounds like you want a conditional join.
looks like you are always joining on the tran year tran month but according to your 2 flags decides the rest of the join
I started something here where I am joining on the tran year / tran month then setting an indicator based on your flags
then just select the rows where this indicator is true.
anyway you can modify it to your needs
WITH t AS (SELECT 1 EmpId,
                  EXTRACT (YEAR FROM TO_DATE ('2010', 'YYYY')) TranYear,
                  EXTRACT (MONTH FROM TO_DATE ('Oct', 'Mon')) TranMon,
                  10 approved_by,
                  EXTRACT (YEAR FROM TO_DATE ('2010', 'YYYY')) ApprovedYear,
                  EXTRACT (MONTH FROM TO_DATE ('Nov', 'Mon')) ApprovedMon
             FROM DUAL
           UNION ALL
           SELECT 2,
                  EXTRACT (YEAR FROM TO_DATE ('2009', 'YYYY')),
                  EXTRACT (MONTH FROM TO_DATE ('Jul', 'Mon')),
                  11,
                  EXTRACT (YEAR FROM TO_DATE ('2009', 'YYYY')),
                  EXTRACT (MONTH FROM TO_DATE ('Dec', 'Mon'))
             FROM DUAL),
     input AS (SELECT EXTRACT (YEAR FROM TO_DATE ('2010', 'YYYY')) TranYear,
                      EXTRACT (MONTH FROM TO_DATE ('Oct', 'Mon')) TranMon,
                      0 tag1,
                      0 tag2
                 FROM DUAL)
SELECT *
  FROM (SELECT t.*,
               tag1,
               tag2,
               CASE tag1 || '.' || tag2
                  WHEN '0.0'
                  THEN
                     CASE WHEN Approved_By IS NOT NULL THEN 1 ELSE 0 END -- if they are both 0 join on  Tran Year, Tran Month and Approved by not null
                  WHEN '0.1'
                  THEN
                     CASE WHEN Approved_By IS NULL THEN 1 ELSE 0 END -- if they are 0,1 then Tran Year, Tran Month and Approved by is null
                  WHEN '0.2'
                  THEN
                     0 -- CASE  --Then both(Approved/unApproved)  i Don't know what this means
                /* WHEN '1.0' then whatever
                    when  '1.1' then whatever
                    when '1.2  then whatever
                  ELSE
                     0
               END
                  ind
          FROM t, input
         WHERE t.TranYear = input.TranYear AND t.TranMon = input.TranMon)
WHERE ind = 1