mysql - MySQL 中的循环和 if

Question

表中有几列，一列是名为“Country”的 varchar 列，另一列是名为“SomeFlag”的 bool 列，我想从记录中过滤所有“SomeFlag”同时为 0 和 1 的国家/地区.
例如，

Record1: country is US, SomeFlag is 0 and some other values.  
Record2: country is US, SomeFlag is 1 and some other values.  
Record3: country is CA, SomeFlag is 1 and some other values.  

那么 US 就是我想要过滤掉的内容，我应该如何构建这个 SQL 查询？
提前致谢。

Answer 1

select Country from T
group by Country
having min(cast(SomeFlag as int)) = max(cast(SomeFlag as int))

或

select Country from T
group by Country
having count(distinct SomeFlag) = 1

或

select Country from T
where not exists (
    select 1 from T
    where SomeFlag = 0
) or not exists (
    select 1 from T
    where SomeFlag = 1
)

或

select Country from T
where Country not in (
    select Country from T
    group by Country
    having
            min(cast(SomeFlag as int)) = 0
        and max(cast(SomeFlag as int)) = 1
)

SomeFlag 中的空值会起作用吗？