1.場合

select...caseが複雑の時

2.運用方法

 1 SELECT * 
 2 FROM stu 
 3  CROSS APPLY ( --like inner join
 4   SELECT TOP 1 * FROM score WHERE stu.stuId=score.stuId ORDER BY score DESC 
 5  ) AS ff
 6  /*
 7  OUTER APPLY ( --like left join
 8   SELECT TOP 1 * FROM score WHERE stu.stuId=score.stuId ORDER BY score DESC 
 9  ) AS ff
10  */

虽然apply性能低,但是也有其用武之地,当需要按照顺序进行连接时,apply是最好的选择。