WHEN内的SQL Case

Question

May be this is silly but can we write a case inside another case's WHEN ?

Below code working for me but I am not sure if this is correct.

SELECT
     (SUM(CASE
            WHEN (
                  CASE
                      WHEN r.status < b.status
                      THEN r.status
                      ELSE b.status
                  END
                 ) = '4' 
            THEN 1
            ELSE 0
         END)
     ) AS WORKED
FROM
    tbl1 r, tbl2 b

All the examples on nested cases are like CASE inside a THEN so I am not sure if this a good practice. Is there a better way to get the same results?

Answer 1

Yes you can. MSDN also informs us that in SQL SERVER, you can only have a maximum of 10 CASE expressions embedded into each other. Oddly enough, a search for ORACLE up negative about this potential limitation. Probably important to note.

Of course, you can also just use more WHEN (up to 255 in ORACLE) statements, too, but that only works if you do not need to nest your logic (such as comparing two different columns values)

Sources: https://msdn.microsoft.com/en-us/library/ms181765.aspx http://www.techonthenet.com/oracle/functions/case.php