Question

我有一张表call_memmo，其中chance_no列为int。还有其他两列is_group1和is_group2都是tinyint类型且互斥。所以我想在一次查询中为max(chance_no)和is_group1=1提取is_group2=1。

我试过了这个查询

select if(is_group1 <> 0, max(chance_no), 0) as max_chance_group1,
       if(is_group2 <> 0, max(chance_no), 0) as max_chance_group2
from call_memmo

结果为

max_chance_group1   max_chance_group2
                0                   3

输出错误，因为max_chance_group1应该是2。

然后我尝试了这个查询

select (select max(chance_no) from call_memmo where is_group1 = 1) as max_chance_group1, 
       (select max(chance_no) from call_memmo where is_group2 = 1) as max_chance_group2

from call_memmo group by is_group1, is_group2

这正确地提供输出但是有多条记录

max_chance_group1   max_chance_group2
                2                   3
                2                   3

我知道我使用的查询不正确，所以任何人都可以帮助我更好的方法并获得单行输出，以便我可以跳过迭代吗？

Answer 1

select (select max(chance_no) from call_memmo where is_group1 = 1) as max_chance_group1, 
       (select max(chance_no) from call_memmo where is_group2 = 1) as max_chance_group2
from call_memmo limit 1

或者您可以将新列分组为

  select (select max(chance_no) from call_memmo where is_group1 = 1) as max_chance_group1, 
(select max(chance_no) from call_memmo where is_group2 = 1) as max_chance_group2 from call_memmo group by max_chance_group1, 
max_chance_group2

Answer 2

尝试不需要分组

select (select max(chance_no) from call_memmo where is_group1 = 1) as max_chance_group1, 
       (select max(chance_no) from call_memmo where is_group2 = 1) as max_chance_group2

将互斥列的多个最大值提取到一行中

2 个答案: