SELECT

  id,

  CASE

    WHEN date_activated > '2011-11-23 18:30:00' THEN 'after'

    WHEN date_activated > '2010-01-20 00:00:00' THEN 'before'

    ELSE 'not yet'

  END AS date_note

FROM table1;

​

SELECT

    CASE 

        WHEN

            column IS NULL OR another_column = 1

        THEN

            'yes' 

        ELSE

            'no' 

    END AS 'MyData'

FROM

    table_name;

SELECT column1,

       CASE

           WHEN condition1 AND condition2 THEN result1

           WHEN condition3 AND condition4 THEN result2

           ELSE result3

       END

FROM your_table;