SQL Server - Use a string that contain single quotes '

How to use a string that contain single quotes '

Problem: Incorrect syntax near ' +


Solution: duplicate the single quotes '' ''


DECLARE @sql nvarchar(max)

SET @sql =
    'SELECT        employee,         FLastName + ''  '' +SLastName + ''  '' + FName + ''  '' +SName + ''  ''
        AS Employee_name 
    '
Note: This example not contains the validation with CASE WHEN IS NULL.