1 CREATE PROCEDURE sys.sp_student
2     @id int,
3     @name varchar(20),
4     @age int
5 AS
6 BEGIN
7     SELECT * from Student WHERE Id=@id
8 END
9 GO

SET @where=‘SELECT * FROM Student WHERE 1=1‘
    if(@id is not null)
        SET @where=@where+‘ AND Id=‘+‘‘‘‘+@id+‘‘‘‘
    if(@name is not null AND @name<>‘‘)
        SET @where=@where+‘ AND Name= ‘+‘‘‘‘+@name+‘‘‘‘
    if(@age is not null)
        SET @where=@where+‘ AND Age=‘+@age
    if(@sex is not null AND @sex <>‘‘)
        SET @where=@where+‘ AND Sex=‘+‘‘‘‘+@sex+‘‘‘‘
    EXEC (@where)

select * from Student 
where
     (Id= @id or @id is null) and
     (Name = @name or @name is null) and
     (Age=@age or @age is null)

SELECT * FROM Student where 
　　Id= ISNULL(@id,Id) AND
　　Name = ISNULL(@name,Name) AND
      Age=ISNULL(@age,Age)