取某个字段值，加以判断

mysql 字段值判断 table1 id man tid 1 first 3 2 second 0 3 three 2 CREATE PROCEDURE dbo.GetNameById @id int, @result nvarchar(50) output AS select man , @tid = tid from students where id =@id if @tid = 0 or @tid is null set @result = “”当前名字为空!”” 如何取到 @tid 字段的值，并加以判断？
	@tid := tid
5分	在非SET语句中=被视为一个比较操作符：
	谢谢您，不行啊，语法错误
	错误代码： 1064 You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near “”:=
5分	select man,tid as @tid from students where id =@id if @tid = 0 or @tid is null set @result = “”当前名字为空!””
10分	select tid into @tid from students where id =@id