Question

I have tables as below

table A

emp_code | emp_name

table B

emp_code | id

table C

emp_code | id

I want to get emp_name so I do:

SELECT a.emp_name 
  FROM A a, B a 
 WHERE a.emp_code = b.emp_code

Now I want to capture a case when id in table B is not null and greater than 0 then it should compare a.emp_code with emp_code from table C (like SELECT c.emp_code FROM C c, B b WHERE c.id = b.id) otherwise do as above.

Answer 1

You could UNION two SELECTs, the first on B excluding records with 0 or null, and the second on C including only records where B has 0 or null.