SQL server use "IF variable LIKE pattern"

Question

Why this doesn't work?

DECLARE @str varchar = '######'

IF @str LIKE '%###%' SELECT 1

but this works

IF '######' LIKE '%###%' SELECT 1

UPDATE

why this works

DECLARE @Comment varchar(255) = '[A-B-C-D]'

IF @Comment LIKE '%[%-%-%-%]%' SELECT 1

however this doesn't work?

DECLARE @Comment nvarchar(255) = '[A-B-C-D]'

IF @Comment LIKE '%[%-%-%-%]%' SELECT 1

Answer 1

Add to your variable type length.

DECLARE @str varchar = '######'

IF @str LIKE '%###%' SELECT 1

is the same as (implicit cast will change it to '#')

DECLARE @str varchar(1) = '######'

/* IF '#' LIKE '%###%' SELECT 1 */
IF @str LIKE '%###%' SELECT 1

This will work:

DECLARE @str varchar(20) = '######'

IF @str LIKE '%###%' SELECT 1