MySQL Tricky Where Clause

时间：2013-07-19 16:16:53

标签： mysql where-clause

我有一个mysql表，其中包含一个名为sequence的列。

这是我的陈述：

SELECT
a.modelyear,
count(*) as yearcount
FROM styles a, jpgs b, models c, divisions d
WHERE d.divisionid = c.divisionid
AND a.styleid = b.styleid
AND c.modelid = a.modelid
AND a.mktclassid in ($this->mktclassids)
AND a.sequence = 0
$this->where
GROUP BY a.modelyear;

上述查询应输出等于此查询的计数：

select count(distinct(modelid)) from styles where mktclassid in ($this->mktclassids)
$this->where

我的问题是为了获得计数的每个唯一的modelid。序列可以等于0或1，但不能同时为两个。 因此，modelid可能有一个序列= 0.如果它不等于0，那么它将等于1。 我需要在where子句中使用if语句。

这就是我认为我需要的：

if modelid has a.sequence = 0, then use a.sequence = 0
else modelid does not have a.sequence = 0, then use a.sequence = 1

我不是一个mysql的家伙很抱歉，如果我不表达我需要的东西.. 基本上，如果modelid没有sequence = 0，那么它将具有sequence = 1

样式表为每个模型提供了许多修剪级别。并且第一个修剪将等于0或1.这是样式表的示例

styleid modelid sequence
350422  25156   1
350425  25156   4
350426  25156   5
350427  25156   7
350428  25156   11
350429  25156   6
350432  25156   9
350433  25156   10
356717  25156   8

styleid modelid sequence
308367  18875   0
308368  18875   1
308369  18875   2
308370  18875   3
308371  18875   4

我正试图从这张表中获得一个独特的模型。 我不相信我可以使用DISTINCT，因为它会影响我的整个查询。

所以你可以看到这个模型没有sequence = 0，所以我需要使用sequence = 1 也许一个包含1或0 ...我不确定 任何帮助是极大的赞赏 感谢

1 个答案:

答案 0 :(得分：1)

你试过吗

...
AND (a.sequence=0 OR a.sequence=1)
...

我会加入而不是使用所有这些WHERE语句来优化此查询。

SELECT
    a.modelyear,
    count(*) as yearcount
FROM
    styles a
    INNER JOIN jpgs b ON (a.styleid = b.styleid)
    INNER JOIN models c ON (c.modelid = a.modelid)
    INNER JOIN divisions d ON (d.divisionid = c.divisionid)
WHERE
    a.mktclassid in ($this->mktclassids)
    AND (a.sequence=0 OR a.sequence=1)
    $this->where
GROUP BY 
    a.modelyear;

上面的查询将获得序列1或0的所有项目，下一个查询带我思考。我将使用查询注释#进行解释，但它应该得到不具有1和0序列的项：

SELECT
    a.modelyear,
    count(*) as yearcount
FROM
    styles a
    INNER JOIN jpgs b ON (a.styleid = b.styleid)
    INNER JOIN models c ON (c.modelid = a.modelid)
    INNER JOIN divisions d ON (d.divisionid = c.divisionid)
WHERE
    a.mktclassid in ($this->mktclassids)
    #above same as previous
    #and where modelid is in modelids either having sequence 0 or 1 but not both:
    AND a.modelid IN (
        #SELECT modelids that have either sequence 0 or 1 but not both
        SELECT
            styles.modelid
        FROM
            styles
        WHERE
            (
                styles.modelid IN (#modelids having sequence 0 but not 1
                    SELECT
                        styles.modelid
                    FROM
                        styles
                    WHERE
                        styles.sequence=0
                    GROUP BY
                        styles.modelid
                ) AND 
                styles.modelid  NOT IN (
                    SELECT
                        styles.modelid
                    FROM
                        styles
                    WHERE
                        styles.sequence=1
                    GROUP BY
                        styles.modelid
                ) 
            )
            OR
            (
                styles.modelid NOT IN (#modelids having sequence 1 but not 0
                    SELECT
                        styles.modelid
                    FROM
                        styles
                    WHERE
                        styles.sequence=0
                    GROUP BY
                        styles.modelid
                ) AND 
                styles.modelid IN (
                    SELECT
                        styles.modelid
                    FROM
                        styles
                    WHERE
                        styles.sequence=1
                    GROUP BY
                        styles.modelid
                ) 
            )
    )
    $this->where
GROUP BY 
    a.modelyear

我希望这不会太混乱

用户声明查询将永远运行。试试这个子查询部分，让我知道它的性能。

        SELECT
            styles.modelid
        FROM
            styles
        WHERE
            (
                styles.modelid IN (
                    SELECT
                        styles.modelid
                    FROM
                        styles
                    WHERE
                        styles.sequence=0
                    GROUP BY
                        styles.modelid
                ) AND 
                styles.modelid  NOT IN (
                    SELECT
                        styles.modelid
                    FROM
                        styles
                    WHERE
                        styles.sequence=1
                    GROUP BY
                        styles.modelid
                ) 
            )
            OR
            (
                styles.modelid NOT IN (
                    SELECT
                        styles.modelid
                    FROM
                        styles
                    WHERE
                        styles.sequence=0
                    GROUP BY
                        styles.modelid
                ) AND 
                styles.modelid IN (
                    SELECT
                        styles.modelid
                    FROM
                        styles
                    WHERE
                        styles.sequence=1
                    GROUP BY
                        styles.modelid
                ) 
            )
  

所以我只是想从表中获得不同的模型，但是优选序列为0或1 - OP 

SELECT
    modelid,
    sequence
FROM
    (
        SELECT
            modelid,
            sequence
        FROM
            styles
        ORDER BY
            sequence ASC
    ) AS sub_query
GROUP BY
    modelid
  

这正是我所需要的。我如何将其作为where子句添加到原始查询中？ - OP 

SELECT
a.modelyear,
count(*) as yearcount
FROM styles a, jpgs b, models c, divisions d
WHERE d.divisionid = c.divisionid
AND a.styleid = b.styleid
AND c.modelid = a.modelid
AND a.mktclassid in ($this->mktclassids)
AND a.modelid IN (
    SELECT
        modelid
    FROM
        (
            SELECT
                modelid,
                sequence
            FROM
                styles
            ORDER BY
                sequence ASC
        ) AS sub_query
    GROUP BY
        modelid
)
$this->where
GROUP BY a.modelyear;

其结果与：

相同 
SELECT
a.modelyear,
count(*) as yearcount
FROM styles a, jpgs b, models c, divisions d
WHERE d.divisionid = c.divisionid
AND a.styleid = b.styleid
AND c.modelid = a.modelid
AND a.mktclassid in ($this->mktclassids)
AND a.modelid IN (
    SELECT
        modelid
    FROM
        styles
    GROUP BY
        modelid
)
$this->where
GROUP BY a.modelyear;

我认为这不是你想要的。你不需要这个作为WHERE子句，但你需要完全更好的查询。其他表是否必要？ $this->where 等同于什么？

在考虑了这个又一个小时后，我想这可能就是你真正想要的。这会将样式表限制为只有一个modelid并将它们排序到最低序列，然后它连接到其他表并应用mktclassid IN子句和$this->where子句：

SELECT
a.modelyear,
count(*) as yearcount
FROM
    (
        SELECT
            *
        FROM
            (
            SELECT
                *
            FROM
                styles
            ORDER BY
                sequence ASC
            ) subquery
        GROUP BY
            modelid
    ) a
    INNER JOIN jpgs b ON (a.styleid = b.styleid)
    INNER JOIN models c ON (c.modelid = a.modelid)
    INNER JOIN divisions d ON (d.divisionid = c.divisionid)
WHERE 
    a.mktclassid in ($this->mktclassids) AND
    $this->where
GROUP BY a.modelyear;

在此之后，我已经完成了，除了 CLARIFY 您的问题之外没有其他建议，请提供sqlFiddle并提供更多预期示例输出。有时你遇到的问题是因为你想要做的事情是以错误的方式处理事情。如果可能的话，总是说明你为什么要做的事情，而不仅仅是这里的问题......其他人可能能够简化过程并提供解决实际问题的解决方案。祝你好运！

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