Try to use coalesce in my query, for example I want the following query
NULLIF() is not a standard SQL function, so it won't work depending on the brand of RDBMS you use.
The equivalent in standard SQL would be:
COALESCE(CASE columnname WHEN '' THEN NULL ELSE columnname END, 'THIS')
Or you might as well do this:
CASE columnname WHEN '' THEN 'THIS' ELSE columnname END