/* Case 1: X = NULL */

declare @i int = null;

set ansi_nulls off;

if @i = null

select 'True' as [Case 1, ansi_nulls OFF]

else

select 'FALSE' as [Case 1, ansi_nulls OFF];

set ansi_nulls on;

if @i = null

select 'True' as [Case 1, ansi_nulls ON]

else

select 'FALSE' as [Case 1, ansi_nulls ON];

if @i is null

select 'True' as [Case 1, ansi_nulls ON, solution]

else

select 'FALSE' as [Case 1, ansi_nulls ON, solution];

go

/* Case 2: CASE X WHEN NULL */

declare @i int = null;

set ansi_nulls off;

select case @i when null then 'True' else 'FALSE' end as [Case 2, ansi_nulls OFF];

set ansi_nulls on;

select case @i when null then 'True' else 'FALSE' end as [Case 2, ansi_nulls ON];

select case when @i is null then 'True' else 'FALSE' end as [Case 2, ansi_nulls ON, solution];

go