Question

I have the following table:

TestTable  
  ColumnA  
  Column1  
  Column2  
  Column3  
  Column4 

I want to write a simple SQL statement that checks ColumnA and depending on whether it is null or not returns certain columns.

Something like (pseudo):

If ColumnA Is Null
  SELECT ColumnA, Column1, Column2 
  FROM TestTable
Else
  SELECT ColumnA, Column3, Column4
  FROM TestTable

Any ideas?

Answer 1

Use SQL CASE expressions:

SELECT
    ColumnA,
    CASE WHEN ColumnA IS NULL THEN Column1 ELSE Column3 END AS ColumnB,
    CASE WHEN ColumnA IS NULL THEN Column2 ELSE Column4 END AS ColumnC
FROM
    TestTable

See:
CASE (SQL-Server Transact-SQL)
CASE Expressions (Oracle)