SQL 面试碰到的一个问题

Question

有一张表，两个字段id和num,如何将这张表的数据行数增加为原来的4倍，值按行翻倍@

Answer 1

表 test
id a1
1 50
2 30
3 40
韬哥赐给你一段机缘吧

select test.id,
(test.a1*(4-(if(bb1=1,1,0)+if(bb2=1,1,0)+if(bb3=1,1,0))))  as aa1
from 
test
,(select 1 as bb1) as b1,(select 1 as bb2) as b2,(select 1 as bb3) as b3
group by test.id,bb1,bb2,bb3 with ROLLUP
having test.id is not null

结果
1 50
1 100
1 150
1 200
2 30
2 60
2 90
2 120
3 40
3 80
3 120
3 160