将同一表上的多个MySQL查询合并为一个

Question

您如何在同一个表上进行多个查询，选择不同的列？

如果有帮助...所有查询在SQL语句的select部分中都有一个公共列。 他们都选择ID ，然后是特定的内容。

因此，每个查询都需要ID和以下任意一个ID ： post_name ， post_title或post_excerpt 。

另外，如果它有助于简化操作。 我正在尝试在这些列中搜索广泛匹配和完全匹配。

因此，在我的示例中，我将在以下几列中寻找：“ floor finish”，“ floor”或“ finish”： post_name ， post_title和post_excerpt 。 全部在同一张表中。

我试图通过UNION完成此任务。

这是我的查询：

Array
(
    [broad] => Array
        (
            [floor] => Array
                (
                    [slugs] => SELECT `ID`, `post_name` FROM tps_3_posts WHERE `post_status` = 'publish' AND `post_name` LIKE '%floor%'
                    [titles] => SELECT `ID`, `post_title` FROM tps_3_posts WHERE `post_status` = 'publish' AND `post_title` LIKE '%floor%'
                    [excerpts] => SELECT `ID`, `post_excerpt` FROM tps_3_posts WHERE `post_status` = 'publish' AND `post_excerpt` LIKE '%floor%'
                )

            [finish] => Array
                (
                    [slugs] => SELECT `ID`, `post_name` FROM tps_3_posts WHERE `post_status` = 'publish' AND `post_name` LIKE '%finish%'
                    [titles] => SELECT `ID`, `post_title` FROM tps_3_posts WHERE `post_status` = 'publish' AND `post_title` LIKE '%finish%'
                    [excerpts] => SELECT `ID`, `post_excerpt` FROM tps_3_posts WHERE `post_status` = 'publish' AND `post_excerpt` LIKE '%finish%'
                )

        )

    [exact] => Array
        (
            [slugs] => SELECT `ID`, `post_name` FROM tps_3_posts WHERE `post_status` = 'publish' AND `post_name` LIKE '%floor-finish%'
            [titles] => SELECT `ID`, `post_title` FROM tps_3_posts WHERE `post_status` = 'publish' AND `post_title` LIKE '%floor finish%'
            [excerpts] => SELECT `ID`, `post_excerpt` FROM tps_3_posts WHERE `post_status` = 'publish' AND `post_excerpt` LIKE '%floor finish%'
        )

    [combined] => ( SELECT `ID`, `post_name` FROM tps_3_posts WHERE `post_status` = 'publish' AND `post_name` LIKE '%floor-finish%' ) UNION ( SELECT `ID`, `post_name` FROM tps_3_posts WHERE `post_status` = 'publish' AND `post_name` LIKE '%floor%' ) UNION ( SELECT `ID`, `post_name` FROM tps_3_posts WHERE `post_status` = 'publish' AND `post_name` LIKE '%finish%' ) UNION ( SELECT `ID`, `post_title` FROM tps_3_posts WHERE `post_status` = 'publish' AND `post_title` LIKE '%floor finish%' ) UNION ( SELECT `ID`, `post_title` FROM tps_3_posts WHERE `post_status` = 'publish' AND `post_title` LIKE '%floor%' ) UNION ( SELECT `ID`, `post_title` FROM tps_3_posts WHERE `post_status` = 'publish' AND `post_title` LIKE '%finish%' ) UNION ( SELECT `ID`, `post_excerpt` FROM tps_3_posts WHERE `post_status` = 'publish' AND `post_excerpt` LIKE '%floor finish%' ) UNION ( SELECT `ID`, `post_excerpt` FROM tps_3_posts WHERE `post_status` = 'publish' AND `post_excerpt` LIKE '%floor%' ) UNION ( SELECT `ID`, `post_excerpt` FROM tps_3_posts WHERE `post_status` = 'publish' AND `post_excerpt` LIKE '%finish%' )
)

但是，上述结果很有趣。 我似乎得到了所有正确的结果，但每个结果值的键（应该是列的名称）始终保持不变。 它总是post_name即使分配给它的值可能是一个post_title或post_excerpt 。

因此，每个结果都有一个ID和post_name 。 基本上，它们的键是错误的，但是值看起来是准确的。

我也尝试过这样的事情：

Array
        (
            [broad] => Array
                (
                    [floor] => SELECT `ID`, `post_name`, `post_title`, `post_excerpt` FROM tps_3_posts WHERE `post_status` = 'publish' AND ( `post_name` LIKE '%floor%' OR `post_title` LIKE '%floor%' OR `post_excerpt` LIKE '%floor' )
                    [finish] => SELECT `ID`, `post_name`, `post_title`, `post_excerpt` FROM tps_3_posts WHERE `post_status` = 'publish' AND ( `post_name` LIKE '%finish%' OR `post_title` LIKE '%finish%' OR `post_excerpt` LIKE '%finish%' )
                )

            [exact] => SELECT `ID`, `post_name`, `post_title`, `post_excerpt` FROM tps_3_posts WHERE `post_status` = 'publish' AND ( `post_name` LIKE '%floor-finish%' OR `post_title` LIKE '%floor finish%' OR `post_excerpt` LIKE '%floor finish%' )
            [combined] => SELECT `ID`, `post_name`, `post_title`, `post_excerpt` FROM tps_3_posts WHERE `post_status` = 'publish' AND ( `post_name` LIKE '%floor-finish%' OR `post_title` LIKE '%floor finish%' OR `post_excerpt` LIKE '%floor finish%' ) UNION (SELECT `ID`, `post_name`, `post_title`, `post_excerpt` FROM tps_3_posts WHERE `post_status` = 'publish' AND ( `post_name` LIKE '%floor%' OR `post_title` LIKE '%floor%' OR `post_excerpt` LIKE '%floor%' )) UNION (SELECT `ID`, `post_name`, `post_title`, `post_excerpt` FROM tps_3_posts WHERE `post_status` = 'publish' AND ( `post_name` LIKE '%finish%' OR `post_title` LIKE '%finish%' OR `post_excerpt` LIKE '%finish%' ))
        )

)

这更符合我要完成的工作。 我希望每个结果都具有ID ， post_excerpt ， post_slug和post_title 。 如果没有匹配项，则将其键显示为空值，或者完全不显示键。

第二次尝试的问题是它只需要在三个所需列之一中进行匹配即可。 因此，如果在post_excerpt匹配，并且在其他任何地方都没有匹配，它将仍然从post_title和post_name post_title值。 因此使结果不准确。

我已经阅读了几个看似相似的问题，但是大多数问题并没有真正可靠的明确答案...或...这些问题/答案更适合于SEPARATE表上的多个查询。

有关在同一表上组合多个MySQL查询的任何指导或建议？

顺便说一句...我在两个示例中都使用“组合”作为我的最终查询，以发送到数据库。

因此，再等等一次...如果一列中没有匹配项，则将其键显示为null或完全从结果中完全省略键。

Answer 1

由于查询中的UNION语句，您获得了错误的“键”。 您具有不同的键名，但是在联合查询的三个不同列之间具有兼容的列类型。 数据库引擎没有抛出错误，而是从第一个查询中选择列名称，然后对所有列使用该名称：

id | post_name # <= column name in first query
1  | "my post"

UNION

id | post_title # <= column name is different, but type is compatible, so UNION succeeds
1  | "my post title"

UNION

id | post_excerpt # <= ditto
1  | "my post excerpt"

会导致：

id | post_name # <= column name from first query
1  | "my post"
1  | "my post title"
1  | "my post excerpt"

这就是你正在经历的。

相反，您可以执行以下操作：

id | post_name | post_title | post_excerpt
1  | "my post" | null       | null        # <= deliberately select nulls for these columns in this query

UNION

id | post_name | post_title      | post_excerpt
1  | null      | "my post title" | null

UNION

id | post_name | post_title | post_excerpt
1  | null      | null       | "my post excerpt"

这将给您以下结果：

id | post_name | post_title      | post_excerpt
1  | "my post" | null            | null
1  | null      | "my post title" | null
1  | null      | null            | "my post excerpt"

在您的表中，一个非常基本的版本可能看起来像：

SELECT ID, post_name, null AS post_title, null AS post_excerpt FROM tps_3_posts

UNION

SELECT ID, null AS post_name, post_title, null AS post_excerpt FROM tps_3_posts

UNION

SELECT ID, null AS post_name, null AS post_title, post_excerpt FROM tps_3_posts

这对于您正在尝试做的事情可能更有用。 如果您想查看它的运行，请使用SQLFiddle 。

Answer 2

正如我在第二种情况下所理解的那样，问题在于只有匹配的列才应具有值，而其他列应为null。 对于这种情况，可以在SELECT中使用IF / ELSE或WHEN语句。 想法是您选择实际值，该列的值对应于期望值，否则为null。

另一个潜在的解决方案是您可以编写例如

SELECT `ID`, `post_name`, `post_title`, 'post_excerpt'

因此，您选择的字符串值是WHERE语句中的条件，以后可以使用该值来了解该行所属的内容。