Question

有没有办法检查表的列中是否存在多个值，即使这些值不在同一行中？

我有这个问题：

select (select country from storage where country = 'Germany' limit 1) as country,
       (select city from storage where city = 'New York City' limit 1) as city,
       (select pet from storage where pet = 'Dog' limit 1) as pet,
       (select profession from storage where profession='owehs9843' limit 1) as profession

此查询可以满足我的需求。如果该值存在于列中，则返回搜索的值，否则返回null。

一种解决方案是执行if语句并在找到时返回1，否则返回0。

但是，我不确定这是检查每列值的正确方法，而不是每行。我希望值存在于某个列的列中，但每列的键值行不需要关联。

Answer 1

刚刚在MySql WorkBench（来自Windows）上对此进行了测试，以下查询在找到值时返回1并且如果没有则返回cero（对于每列）。

select if(sum(country = 'Germany') = 0, 0, 1) as country,
       if(sum(city = 'New York City') = 0, 0, 1) as city,
       if(sum(pet = 'Dog') = 0, 0, 1) as pet,
       if(sum(profession = 'owehs9843') = 0, 0, 1) as profession
from storage;

检查表MySQL中是否存在值

1 个答案: