How to use NULL or empty string in SQL

I would like to know how to use NULL and an empty string at the same time in a WHERE clause in SQL Server. I need to find records that have either null values or an empty string. Thanks.

Select *
From Table
Where (col is null or col = '')

Or

Select *
From Table
Where IsNull(col, '') = ''

If you need it in SELECT section can use like this.

SELECT ct.ID, 
       ISNULL(NULLIF(ct.LaunchDate, ''), null) [LaunchDate]
FROM   [dbo].[CustomerTable] ct

You can replace the null with your substitution value.

You can simply do this:

SELECT *
FROM   yourTable
WHERE  yourColumn IS NULL OR yourColumn = ''

SELECT *
FROM   TableName
WHERE  columnNAme IS NULL OR 
       LTRIM(RTRIM(columnName)) = ''