SELECT Emp_NUM, Full_name, Mother_Name, Date_of_Birth, Province_of_birth, Job
FROM  [Emp Main Table]
WHERE (Full_name LIKE '%' + @Full_name + '%' OR Full_name IS NULL) AND
(Mother_Name LIKE '%' + @Mother_Name + '%' OR Mother_Name IS NULL) AND
(Date_of_Birth LIKE '%' + @Date_of_Birth + '%' OR Date_of_Birth IS NULL)

SELECT [Emp_NUM]
,[Full_name]
,[Mother_Name]
,[Date_of_Birth]
,[Province_of_birth]
,[Job]
FROM [Emp Main Table]
WHERE ([Full_name] LIKE '%' + @Full_name + '%' OR @Full_name IS NULL)
AND ([Mother_Name] LIKE '%' + @Mother_Name + '%' OR @Mother_Name IS NULL)
AND ([Date_of_Birth] LIKE '%' + @Date_of_Birth + '%' OR @Date_of_Birth IS NULL)

rtrim(coalesce(@Full_name, '')) = ''

@Full_name is null