选择中的条件语句

Question

Here's what i wanna do

Select X, Y, if Z IS NULL THEN ( select something ) else Z

Basically I want to select the 'Z' if it's null I want to select another value, can someone please suggest a code example with a case or something that I can follow through it ?

Answer 1

Do you want coalesce() ?

Select X, Y,
       coalesce(z, <something else>) as z

Answer 2

Select X, Y, NVL(Z, showThis) as Z

will return showThis if Z is null in ORACLE

Select X, Y, ISNULL(Z, showThis) as Z

will return showThis if Z is null in SQL-SERVER

Answer 3

Choose with CASE:

select 
  X, Y, 
  case 
    when Z is null then (select something)
    else (select something else)
  end as col
from tablename