nice question , it depends on ansi_nulls settings

Statement 1 -

set ansi_nulls off

SELECT CASE COL1 WHEN NULL THEN 'Is Null'

WHEN '0' THEN 'Is Zero'

WHEN '1' THEN 'Is One'

WHEN '2' THEN 'Is Two'

END

FROM

(

SELECT NULL AS Col1

UNION

SELECT '0' AS Col1

UNION

SELECT '1' AS Col1

UNION

SELECT '2' AS Col1

) TMP

statement 2 -

set ansi_nulls on

SELECT CASE COL1 WHEN NULL THEN 'Is Null'

WHEN '0' THEN 'Is Zero'

WHEN '1' THEN 'Is One'

WHEN '2' THEN 'Is Two'

END

FROM

(

SELECT NULL AS Col1

UNION

SELECT '0' AS Col1

UNION

SELECT '1' AS Col1

UNION

SELECT '2' AS Col1

) TMP

Regards Deepak