我有一个表table1,其中有3列column1,column2和column3.

column1和column2是一个带有2个其他表的FOREIGN KEY.但是,第3列中的数据来自n个表.

对于例如让我们考虑一下Facebook.要显示活动,它可能会维护一个表,该表可能具有user1 photoliked photo1或user1 statusliked status1.所以在这种情况下,column3不能是具有特定表的FOREIGN KEY.

现在有两种获取真实数据的方法 –

第一路 –

SELECT user_id,verb_id,CASE WHEN verb_id = photoliked THEN
            (SELECT photo_name FROM photos WHERE photo_id = column3) -- getting the desired data from the third column
         WHEN verb_id = statusliked THEN
            (SELECT status FROM statustable WHERE status_id = column3) 
         ELSE '' END AS performedon
FROM table1
     JOIN table2 ON user_id = user_id  -- joining the first column
     JOIN table3 ON verb_id = verb_id  -- joining the second column

第二路 –

SELECT user_id,CASE WHEN verb_id = photoliked THEN
            p.photo_name
         WHEN verb_id = statusliked THEN
            s.status
         ELSE '' END AS performedon
FROM table1
     JOIN table2 ON user_id = user_id  -- joining the first column
     JOIN table3 ON verb_id = verb_id  -- joining the second column
     LEFT JOIN photos p ON p.photo_id = column3  -- joining the column3 with specific table 
     LEFT JOIN statustable s ON s.status_id = column3

题

检索数据的两种方法中哪一种更好？
哪两个查询更便宜？