如何用条件清晰的SQL查询

Question

简单数据库：

street     | age
1st st     | 2
2nd st     | 3
3rd st     | 4
3rd st     | 2

我想构建一个返回DISTINCT街道名称的查询，但仅适用于那些没有人超过3的家庭。

所以结果将是：

 street        | age
    1st st     | 2
    2nd st     | 3

我该怎么做？我知道DISTINCT，但现在如何为所有与DISTINCT匹配的记录条件化

Answer 1

假设表的名称是＆＃39; tab＆＃39;。然后你可以尝试：

select distinct street from tab where street not in (select street from tab where age>3);

我创建了一个sql小提琴，您可以在其中查看结果： http://sqlfiddle.com/#!9/2c513d/2

Answer 2

没有人超过3的家庭的街道名称不同：

SELECT street
FROM table
GROUP BY street
HAVING COUNT(1) <= 3

Answer 3

USE GROUP BY

Select Street
from yourtable
group by street
Having sum(age)<=3

使用NOT EXISTS

可以实现另一种方式

SELECT *
FROM yourtable a
WHERE NOT EXISTS
    (SELECT street
     FROM yourtable b
     WHERE age > 3
       AND a.street = b.street)

Answer 4

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