Question

我有一个名为train的表，其中包含列号，arrival_station，depart_station

我填写了这个，并希望找到只为爱丁堡服务的火车（即所有从火车站出发的火车只抵达爱丁堡）我想使用嵌套查询并使用not exists运算符。

到目前为止，我已经尝试过..

SELECT depart_station
FROM train
WHERE arrive_station = "edinburgh" 
  AND NOT EXISTS
  (
    SELECT arrive_station
    FROM train
    WHERE arrive_station != "edinburgh"
  );

Answer 1

您需要以某种方式将嵌套查询与外部查询相关联，因此，如果编号是列号，则您需要在表中添加别名并添加AND t1.number = t2.number。

SELECT  depart_station
FROM    train t1
WHERE   arrive_station = "edinburgh" 
AND     NOT EXISTS
        (
            SELECT  arrive_station
            FROM    train t2
            WHERE   t2.arrive_station != "edinburgh"
            AND     t1.number = t2.number
        );

Answer 2

为什么需要使用exists运算符？当然，OR就足够了：

select *
from train
where depart_station = 'Edinburgh' or arrive_station = 'Edinburgh';

Answer 3

如果我理解你的问题，你只对到达爱丁堡的任何火车路线感兴趣。所以这样做：

SELECT * FROM train WHERE arrive_station = "Edinburgh"

将此与“不存在”结合使用＆＃39;表达式，创建一个其他路由表，是多余的;放下那部分。

Answer 4

尝试，

SELECT depart_station
FROM train
WHERE arrive_station = "edinburgh" 
AND depart_station NOT IN (
    SELECT depart_station
    FROM train
    WHERE arrive_station != "edinburgh" 
)

检查this SQLFiddle

Answer 5

SELECT  depart_station
FROM    train t1
WHERE   arrive_station = "edinburgh" 
AND     NOT EXISTS
        (
            SELECT  arrive_station
            FROM    train t2
            WHERE   t2.arrive_station != "edinburgh"
            AND     t1.number = t2.number
        );

查询中存在非常惊人的逻辑。它可以解决为：

select depart_station from train order by depart_station

但我有一个逻辑，这也解决了我的问题。我的问题有点不同，但无论如何，这确实提供了一个信号。

SQL嵌套查询（不存在）

5 个答案: