Hai diversi tipi di dati
declare @str1 as varchar(10)
declare @str2 as nvarchar(10)
set @str1 = '123456'
set @str2 = '123456'
select
hashbytes('md5', @str1) as 'varchar',
hashbytes('md5', @str2) as 'nvarchar'
Risultato
varchar nvarchar
0xE10ADC3949BA59ABBE56E057F20F883E 0xCE0BFD15059B68D67688884D7A3D3E8C