MySql条件组

Question

请考虑我的表(这只是一个简化版本,在我的项目中,我有600,000多条记录):

Id  TransactionId   TransactionTypeId   Description
1   1               1                   Description1
2   1               1                   Description2
3   1               2                   Description3
4   1               2                   Description4
5   1               1                   Description5
6   1               2                   Description6
7   2               1                   Description7
8   2               1                   Description8
9   2               2                   Description9
10  2               2                   Description10

我需要做的是什么时候TransactionTypeId = 1,我需要从该表中获取最新数据.否则,什么时候TransactionTypeId <> 1,我需要得到它们.

对于这个例子,我有这个查询:

SELECT MAX(T.Id)
    , SUBSTRING_INDEX(GROUP_CONCAT(T.TransactionId ORDER BY T.Id DESC), ',', 1) AS TransactionId
    , SUBSTRING_INDEX(GROUP_CONCAT(T.TransactionTypeId ORDER BY T.Id DESC), ',', 1) AS TransactionTypeId
    , SUBSTRING_INDEX(GROUP_CONCAT(T.Description ORDER BY T.Id DESC), ',', 1) AS Description    
FROM Transactions T
GROUP BY T.TransactionId
    , CASE WHEN T.TransactionTypeId = 1 THEN T.TransactionTypeId END
ORDER BY T.TransactionId, T.TransactionTypeId

我期望的结果将是:

Id  TransactionId   TransactionTypeId   Description
5   1               1                   Description5
3   1               2                   Description3
4   1               2                   Description4
6   1               2                   Description6
8   2               1                   Description8
9   2               2                   Description9
10  2               2                   Description10

但我的问题是,即使TransactionTypeId <> 1查询仍然将它们分组.

我的查询返回:

Id  TransactionId   TransactionTypeId   Description
5   1               1                   Description5
6   1               2                   Description6
8   2               1                   Description8
10  2               2                   Description10

我知道我可以UNION在这里使用,对TransactionTypeId列进行单独查询,但我不能,我花了5分多钟才得到结果.有没有可能(如果没有,我别无选择,只能使用UNION)解决这个问题的方法？

谢谢 :)

更新#1

这是我使用时的查询UNION.

SELECT Transaction.Id
    , Transaction.TransactionId
    , Transaction.TransactionTypeId
    , Transaction.Description
FROM (
    SELECT MAX(T.Id)
        , SUBSTRING_INDEX(GROUP_CONCAT(T.TransactionId ORDER BY T.Id DESC), ',', 1) AS TransactionId
        , SUBSTRING_INDEX(GROUP_CONCAT(T.TransactionTypeId ORDER BY T.Id DESC), ',', 1) AS TransactionTypeId
        , SUBSTRING_INDEX(GROUP_CONCAT(T.Description ORDER BY T.Id DESC), ',', 1) AS Description
    FROM Transactions T
    WHERE T.TransactionTypeId = 1
    GROUP BY T.TransactionId

    UNION

    SELECT T.Id
        , T.TransactionId
        , T.TransactionTypeId
        , T.Description
    FROM Transactions T
    WHERE T.TransactionTypeId <> 1
) Transaction
ORDER BY Transaction.TransactionId, Transaction.TransactionTypeId

Answer 1

试试这个

    SELECT MAX(T.Id)
    , SUBSTRING_INDEX(GROUP_CONCAT(T.TransactionId ORDER BY T.Id DESC), ',', 1) AS TransactionId
    , SUBSTRING_INDEX(GROUP_CONCAT(T.TransactionTypeId ORDER BY T.Id DESC), ',', 1) AS TransactionTypeId
    , SUBSTRING_INDEX(GROUP_CONCAT(T.Description ORDER BY T.Id DESC), ',', 1) AS Description    
FROM Transactions T
GROUP BY  CASE WHEN T.TransactionTypeId = 1 THEN CONCAT(T.TransactionId,'-',T.TransactionTypeId) ELSE T.Id END
ORDER BY T.TransactionId, T.TransactionTypeId