表 b
id age
3 88
5 77
7 55
8 33select s0.id s0_id,s0.age s0_age ,s1.id s1_id,s1.age s1_age
from b as s0, b as s1
where s0.id<s1.id and s0.age>s1.age
group by s0.age结果
s0_id s0_age s1_id s1_age
7 55 8 33
5 77 7 55
3 88 5 77 select s0.id s0_id,s0.age s0_age ,s1.id s1_id,s1.age s1_age
from b as s0, b as s1
where s0.id<s1.id and s0.age>s1.age
group by s1.age结果
s0_id s0_age s1_id s1_age
3 88 8 33
3 88 7 55
3 88 5 77 select s0.id s0_id,s0.age s0_age ,s1.id s1_id,s1.age s1_age
from b as s0, b as s1
where s0.id<s1.id and s0.age>s1.age
group by s0.age,s1.age
结果
s0_id s0_age s1_id s1_age
7 55 8 33
5 77 8 33
5 77 7 55
3 88 8 33
3 88 7 55
3 88 5 77 select s0.id s0_id,s0.age s0_age ,s1.id s1_id,s1.age s1_age
from b as s0, b as s1
where s0.id<s1.id and s0.age>s1.age
group by age
和
select s0.id s0_id,s0.age s0_age ,s1.id s1_id,s1.age s1_age
from b as s0, b as s1
where s0.id<s1.id and s0.age>s1.age
group by b.age
都提示错误困惑中……………………请高人指点
id age
3 88
5 77
7 55
8 33select s0.id s0_id,s0.age s0_age ,s1.id s1_id,s1.age s1_age
from b as s0, b as s1
where s0.id<s1.id and s0.age>s1.age
group by s0.age结果
s0_id s0_age s1_id s1_age
7 55 8 33
5 77 7 55
3 88 5 77 select s0.id s0_id,s0.age s0_age ,s1.id s1_id,s1.age s1_age
from b as s0, b as s1
where s0.id<s1.id and s0.age>s1.age
group by s1.age结果
s0_id s0_age s1_id s1_age
3 88 8 33
3 88 7 55
3 88 5 77 select s0.id s0_id,s0.age s0_age ,s1.id s1_id,s1.age s1_age
from b as s0, b as s1
where s0.id<s1.id and s0.age>s1.age
group by s0.age,s1.age
结果
s0_id s0_age s1_id s1_age
7 55 8 33
5 77 8 33
5 77 7 55
3 88 8 33
3 88 7 55
3 88 5 77 select s0.id s0_id,s0.age s0_age ,s1.id s1_id,s1.age s1_age
from b as s0, b as s1
where s0.id<s1.id and s0.age>s1.age
group by age
和
select s0.id s0_id,s0.age s0_age ,s1.id s1_id,s1.age s1_age
from b as s0, b as s1
where s0.id<s1.id and s0.age>s1.age
group by b.age
都提示错误困惑中……………………请高人指点
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有两个,所以mySQL不知道你要用哪个。[align=center]==== 思想重于技巧 ====
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我是想问group by s0.age ,group by s1.age 和 group by s0.age,s1.age的联系和区别 从中想更加多了解
group by 的语义
其中很困惑的是 group by s0.age,s1.age 如果让我手写 我真不知道用什么思路才能写出答案
其中我感觉很像用for()循环(java中)把条件遍历了一遍
还有感觉group by的作用不光是遍历条件 还有order by的作用还有 我认为as语句 其实就是多加了个副本 as s0 就是系统复制b到新表s0中(内存中) as s1 就是复制b表到s1中
凭借这个逻辑应该还有个原始表b 才对啊
刚才我还试了试 group by s0.b.age(依照2楼的逻辑)也不行
晕了~
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ActiveX Data Objects 2.5 Reference 下载
数据库系统概论PPT[align=center]==== 思想重于技巧 ====
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