ansi-sql - 为投标编写 SQL 查询

Question

我该如何为此编写查询？我不是用 SQL 编写这么多复杂查询的专家。我忘了在这里提到出价 3、4。

Answer 1

根据大卫的查询，消除重复出价并通过支票类型进行限制。

SELECT
   a.bid, min(a.time) checkin, ISNULL(min(b.time), '') checkout
FROM
   myTable a
LEFT JOIN
   myTable b ON a.bid = b.bid
WHERE
   a.type = "Check In"
   AND
   b.type = "Check Out"
GROUP BY
   a.bid
ORDER BY
   a.time

Answer 2

SELECT
   a.bid, a.time checkin, ISNULL(b.time, '') checkout
FROM
   myTable a
LEFT JOIN
   myTable b ON a.bid = b.bid AND b.type = 'Check Out'
WHERE
   a.type = 'Check In'
ORDER BY
   a.time

编辑

为了回应您的评论，看到有多个相同的记录bid，并且您只希望在输出中每个记录一个bid，您需要指定输出中需要哪些记录。当有多个时，您如何决定选择哪个值？如果您总是想要最早签到和最晚结帐，您可以执行以下操作：

SELECT
    a.bid,
    MIN(a.time) checkin,
    ISNULL((SELECT
              MAX(time)
           FROM
              myTable
           WHERE
              bid = a.bid
              AND type = 'Check Out'), '') checkout
FROM
    myTable a
WHERE
    a.type = 'Check In'
GROUP BY
    a.bid

如果那不是您想要的；调整使用MIN和MAX适应您的需要。

Answer 3

这将找到每个投标 ID 的最短签入和签出时间。

select bid, 
(select min(time) from table b where a.bid = b.bid and type = "Check In") as CheckIn,
(select min(time) from table c where a.bid = c.bid and type = "Check Out") as CheckOut
from table c
group by c.bid

Answer 4

我想你正在寻找这样的东西：

SELECT 
    `bid`, 
    MAX(IF(`type` = 'Check In', `time`, NULL)) AS `CheckIn`, 
    MAX(IF(`type` = 'Check Out', `time`, NULL)) AS `CheckOut` 
FROM `yourtable` 
GROUP BY `bid`