Question

情况是我需要选择一个与table1不同的字段（没有重复项），并使用结果作为键从另一个table2中进行选择。我需要在一个查询中。这可能吗？！

table1：hID，hName，hLocation table2：hID，hFrom，hTo，hRate，hRoomType，hMeals

我想更正此查询的版本：

SELECT
    *
FROM
    table1
JOIN (
    DISTINCT
        hID
    FROM
        table2
    WHERE
        hRoomType = Double Room
ON table1.hID = table2.hID)

预期结果：所有提供双人间的酒店都非常感谢 -

感谢您的帮助！

Answer 1

你的问题很模糊，令人困惑。这是你在找什么：

SELECT hID, name, location
FROM table2
INNER JOIN table1
ON table1.hID = table2.hID
GROUP BY table2.hID;

Answer 2

这是实现这一目标的骨架：

SELECT
    * -- Don't forget to list the requested fields instead of using `*`!
FROM (
    -- This is the distinct list from table1
    SELECT DISTINCT
        id
    FROM
        table1 T1
) DT1
INNER JOIN table2 T2
    ON T1.id = T2.reference_to_t1_id

另一种解决方案，如果您不想从table1中检索任何列：

    SELECT
        * -- Don't forget to list the requested fields instead of using `*`!
    FROM
        table2 T2
    WHERE
        -- Sais that get all record from table2 where this condition matches
        -- at least one record
        EXISTS (
            SELECT 1 FROM table1 T1 WHERE T1.id = T2.reference_to_t1_id
        )

对于您的表格和问题

SELECT
    hID, hName, hLocation
FROM
    table1 T1
WHERE
    EXISTS (
        SELECT 1 FROM
            table2 T2
        WHERE
            T1.hID = T2.hID
            AND T.hRoomType = 'Double' -- Assuming that this is the definition of double rooms
    )

从表中选择基于select另一个表的不同

2 个答案: