Question

我对这个问题的答案非常复杂：

Select a record just if the one before it has a lower value

大约3周前。

现在我很难改变这个问题。

所以现在这是此查询的最终版本：

SELECT  a.ID, DATE_FORMAT(a.Time,'%d/%m/%y') AS T, a.SerialNumber, 
    b.Remain_Toner_Black BeforeCount,
    a.Remain_Toner_Black AfterCount
FROM    
    (
        SELECT  a.ID, 
                a.Time, 
                a.SerialNumber, 
                a.Remain_Toner_Black,
                (
                    SELECT  COUNT(*)
                    FROM    Reports c
                    WHERE   c.SerialNumber = a.SerialNumber AND
                            c.ID <= a.ID) AS RowNumber
        FROM    Reports a
    ) a
    LEFT JOIN
    (
        SELECT  a.ID, 
                a.Time, 
                a.SerialNumber, 
                a.Remain_Toner_Black,
                (
                    SELECT  COUNT(*)
                    FROM    Reports c
                    WHERE   c.SerialNumber = a.SerialNumber AND
                            c.ID <= a.ID) AS RowNumber
        FROM    Reports a
    ) b ON a.SerialNumber = b.SerialNumber AND
            a.RowNumber = b.RowNumber + 1
WHERE b.Remain_Toner_Black < a.Remain_Toner_Black AND b.Remain_Toner_Black >= 0

完成后需要 0.0002 秒。

我想要的是编辑此查询的最后一行，所以它将是：

WHERE month(a.Time) = ".$i." AND b.Remain_Toner_Black < a.Remain_Toner_Black AND b.Remain_Toner_Black >= 0

但是，查询需要 6.9047 秒才能完成。

我该如何添加： 月（a.Time）=“。$ i。” 以最有效的方式查询？

Answer 1

考虑到这一点，以下方法可能是比您已经使用的基本选择更快捷的方式： -

SELECT AfterSub.ID, 
    AfterSub.SerialNumber, 
    BeforeSub.Remain_Toner_Black BeforeCount,
    AfterSub.Remain_Toner_Black AfterCount
FROM
(
    SELECT ID, SerialNumber, Remain_Toner_Black, @Counter1:=@Counter1+1 AS SeqCnt
    FROM TableName
    CROSS JOIN (SELECT @Counter1:=0) Sub1
    ORDER BY SerialNumber, ID
) AfterSub
INNER JOIN
(
    SELECT ID, SerialNumber, Remain_Toner_Black, @Counter2:=@Counter2+1 AS SeqCnt
    FROM TableName
    CROSS JOIN (SELECT @Counter2:=1) Sub2
    ORDER BY SerialNumber, ID
) BeforeSub
ON BeforeSub.SerialNumber = AfterSub.SerialNumber
AND BeforeSub.SeqCnt = AfterSub.SeqCnt
WHERE   AfterSub.Remain_Toner_Black > BeforeSub.Remain_Toner_Black
ORDER BY AfterSub.SerialNumber, AfterSub.ID

在这里检查月份的问题是以下项目可能在不同的月份，这取决于计数。

您可以尝试： -

SELECT AfterSub.ID, 
    AfterSub.SerialNumber, 
    BeforeSub.Remain_Toner_Black BeforeCount,
    AfterSub.Remain_Toner_Black AfterCount
FROM
(
    SELECT ID, SerialNumber, Remain_Toner_Black, @Counter1:=@Counter1+1 AS SeqCnt
    FROM TableName
    CROSS JOIN (SELECT @Counter1:=0) Sub1
    ORDER BY SerialNumber, ID
) AfterSub
INNER JOIN
(
    SELECT ID, SerialNumber, Remain_Toner_Black, @Counter2:=@Counter2+1 AS SeqCnt
    FROM TableName
    CROSS JOIN (SELECT @Counter2:=1) Sub2
    ORDER BY SerialNumber, ID
) BeforeSub
ON BeforeSub.SerialNumber = AfterSub.SerialNumber
AND BeforeSub.SeqCnt = AfterSub.SeqCnt
AND AfterSub.Remain_Toner_Black > BeforeSub.Remain_Toner_Black
WHERE month(BeforeSub.Time) = ".$i." 
ORDER BY AfterSub.SerialNumber, AfterSub.ID

但这不会使用索引（但我希望的行数很少，所以我希望不是问题。）

您可以选择获取序列号，然后在加入下个月之前仅检查该月的项目： -

SELECT AfterSub.ID, 
    AfterSub.SerialNumber, 
    BeforeSub.Remain_Toner_Black BeforeCount,
    AfterSub.Remain_Toner_Black AfterCount
FROM
(
    SELECT ID, SerialNumber, Remain_Toner_Black, @Counter1:=@Counter1+1 AS SeqCnt
    FROM TableName
    CROSS JOIN (SELECT @Counter1:=0) Sub1
    ORDER BY SerialNumber, ID
) AfterSub
INNER JOIN
(
    SELECT ID, SerialNumber, Remain_Toner_Black, SeqCnt
    FROM
    (
        SELECT ID, SerialNumber, Remain_Toner_Black, `Time`, @Counter2:=@Counter2+1 AS SeqCnt
        FROM TableName
        CROSS JOIN (SELECT @Counter2:=1) Sub2
        ORDER BY SerialNumber, ID
    ) BeforeSub
    WHERE month(BeforeSub.Time) = ".$i." 
) BeforeSub
ON BeforeSub.SerialNumber = AfterSub.SerialNumber
AND BeforeSub.SeqCnt = AfterSub.SeqCnt
AND AfterSub.Remain_Toner_Black > BeforeSub.Remain_Toner_Black
ORDER BY AfterSub.SerialNumber, AfterSub.ID

（注意，最后2个选项都未经过测试）

修改

将年/月检查添加到2个子选择中。但是，由于日期格式化以执行此检查，我不确定索引是否有用： -

SELECT AfterSub.ID, 
    AfterSub.SerialNumber, 
    BeforeSub.Remain_Toner_Black BeforeCount,
    AfterSub.Remain_Toner_Black AfterCount
FROM
(
    SELECT ID, SerialNumber, Remain_Toner_Black, @Counter1:=@Counter1+1 AS SeqCnt
    FROM TableName
    CROSS JOIN (SELECT @Counter1:=0) Sub1
    WHERE DATE_FORMAT(`Time`,'%Y %m') >= '2013 01' 
    ORDER BY SerialNumber, ID
) AfterSub
INNER JOIN
(
    SELECT ID, SerialNumber, Remain_Toner_Black, `Time`, @Counter2:=@Counter2+1 AS SeqCnt
    FROM TableName
    CROSS JOIN (SELECT @Counter2:=1) Sub2
    WHERE DATE_FORMAT(`Time`,'%Y %m') = '2013 01' 
    ORDER BY SerialNumber, ID
) BeforeSub
ON BeforeSub.SerialNumber = AfterSub.SerialNumber
AND BeforeSub.SeqCnt = AfterSub.SeqCnt
AND AfterSub.Remain_Toner_Black > BeforeSub.Remain_Toner_Black
ORDER BY AfterSub.SerialNumber, AfterSub.ID

在子选择中使用日期（这意味着计算当月的最后一天）可能更有效： -

SELECT AfterSub.ID, 
    AfterSub.SerialNumber, 
    BeforeSub.Remain_Toner_Black BeforeCount,
    AfterSub.Remain_Toner_Black AfterCount
FROM
(
    SELECT ID, SerialNumber, Remain_Toner_Black, @Counter1:=@Counter1+1 AS SeqCnt
    FROM TableName
    CROSS JOIN (SELECT @Counter1:=0) Sub1
    WHERE `Time` >= '2013-01-01' 
    ORDER BY SerialNumber, ID
) AfterSub
INNER JOIN
(
    SELECT ID, SerialNumber, Remain_Toner_Black, `Time`, @Counter2:=@Counter2+1 AS SeqCnt
    FROM TableName
    CROSS JOIN (SELECT @Counter2:=1) Sub2
    WHERE `Time` BETWEEN '2013-01-31' AND '2013-01-31'
    ORDER BY SerialNumber, ID
) BeforeSub
ON BeforeSub.SerialNumber = AfterSub.SerialNumber
AND BeforeSub.SeqCnt = AfterSub.SeqCnt
AND AfterSub.Remain_Toner_Black > BeforeSub.Remain_Toner_Black
ORDER BY AfterSub.SerialNumber, AfterSub.ID

Answer 2

请在A.time上放置索引并使用此

SELECT  a.ID, DATE_FORMAT(a.Time,'%d/%m/%y') AS T, a.SerialNumber, 
    b.Remain_Toner_Black BeforeCount,
    a.Remain_Toner_Black AfterCount
FROM    
    (
        SELECT  a.ID, 
                a.Time, 
                a.SerialNumber, 
                a.Remain_Toner_Black,
                month(a.time) as Month
                (
                    SELECT  COUNT(*)
                    FROM    Reports c
                    WHERE   c.SerialNumber = a.SerialNumber AND
                            c.ID <= a.ID) AS RowNumber
        FROM    Reports a
    ) a
    LEFT JOIN
    (
        SELECT  a.ID, 
                a.Time, 
                a.SerialNumber, 
                a.Remain_Toner_Black,
                (
                    SELECT  COUNT(*)
                    FROM    Reports c
                    WHERE   c.SerialNumber = a.SerialNumber AND
                            c.ID <= a.ID) AS RowNumber
        FROM    Reports a
    ) b ON a.SerialNumber = b.SerialNumber AND
            a.RowNumber = b.RowNumber + 1
WHERE a.month = ".$i." AND b.Remain_Toner_Black < a.Remain_Toner_Black AND b.Remain_Toner_Black >= 0`

Answer 3

我不确定这个答案是否会解决你的问题，但我认为如果你追加这个条件月（a.Time）=“。$ i。”在两个子查询中，即子查询“a”和子查询“b”，它可能有助于提高查询的性能。

如果前面的记录具有按月过滤的较低值，则选择一条记录

3 个答案: