将同一个表上的多个MySQL查询合并为一个

Question

如何在同一个表上进行多个查询，选择不同的列？

如果它有帮助......所有查询在SQL语句的选择部分都有一个共同的列。他们都选择了ID，然后是特定的东西。

因此，每个查询需要ID和以下任一项：post_name,post_title或post_excerpt。

此外，如果它有助于简化事情。我正在尝试在这些列中搜索广泛匹配项和精确匹配项。

所以在我的示例中，我将查找：“floor finish”，“floor”或“finish”在以下列中：post_name,post_title和post_excerpt。全部在同一张表内。

我试图用UNION来实现这个。

这里是我的查询：

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%') 
) 

然而，上述结果是有趣的。我似乎得到所有正确的结果，除了每个结果值（应该是列的名称）的关键字始终保持不变。即使分配给它的值可能是post_title或post_excerpt，它始终为post_name。

所以每个结果都有一个ID和post_name。基本上他们的钥匙是错的，但是这些数值似乎是准确的。

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%')) 
     ) 

) 

这是沿着什么，我试图完成的线条更。我希望每个结果都有ID,post_excerpt,post_slug和post_title。如果没有匹配，则显示它们的键值为空，或者完全不显示该键。

第二次尝试的问题是，它只需要三个所需列中的一个匹配。因此，如果它匹配post_excerpt而没有其他地方，它仍然会从post_title和post_name中提取值。从而导致结果不准确。

我已经阅读了几个似乎是类似的问题，但大多数都没有真正明确的答案......或者...问题/答案更适合于SEPARATE表上的多个查询。

关于在同一个表上组合多个MySQL查询的任何指导或建议？

BY THE WAY ...我在我的例子中使用“组合”作为我的最终查询发送到数据库。

所以再一次......如果列中没有匹配，则显示它们为空或完全忽略结果中的键。

Answer 1

由于查询中的UNION语句，您得到错误的“密钥”。您有不同的键名称，但是三个不同列之间的兼容列类型是联合查询。而不是抛出一个错误，数据库引擎刚刚从第一个查询选择列名和使用，对所有的人：

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" 

这是你是什么经历。

相反，你可以这样做：

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" 

这将使你类似的结果：

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

随着你的表中，这是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 

这可能更适用于您正在尝试做的事情。 Here's a SQLFiddle如果你想看到它的行动。

Answer 2

正如我在第二种情况下所理解的那样，问题是只有匹配的列应该有值，而其他的应该为空。对于这种情况，您可以在SELECT中使用IF/ELSE或WHEN语句。这个想法是你选择的实际值是该列对应于期望值的值，否则为null。

另一个可能的解决方案是你可以编写例如

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

因此，您选择WHERE语句中条件的字符串值，稍后可以使用该值来了解该行属于哪个属性。