mysql - 如果字段包含分隔符则拆分并保留相关行值 MySQL 查询

Question

该表的架构是:

CREATE TABLE `authors` (
  `authorid` int(10) NOT NULL AUTO_INCREMENT,
  `emailaddress` varchar(255) DEFAULT NULL,
  'send' int(1) DEFAULT '0',
  `status` int(1) DEFAULT '0',
  PRIMARY KEY (`authorid`),
  UNIQUE KEY `authorid` (`authorid`) USING BTREE
) ENGINE=MyISAM AUTO_INCREMENT=0 DEFAULT CHARSET=latin1;

示例数据:

 123    john@smith.com;sue@test.org                    1
5271    sally@john.doe                                 0
 834    jacob@tom.smith;foo@bar.net; big@data.cow      1
  27    tuesday@rubys.eat                              1
1977    (null)                                         0
 224                                                   1
  88    miles@per.hour                                 1

注意:上面的(null)不是文本null，而是实际的null值

我想要的是一个可以从第二列获取数据并返回结果集的查询，如下所示:

  id email
------------------------
 123 john@smith.com
 123 sue@test.org
5271 sally@john.doe
 834 jacob@tom.smith
 834 foo@bar.net
 834 big@data.cow
  27 ruby@tuesdays.eat
  88 miles@per.hour

我正在寻找更通用的东西，例如 this example for SQL Server

SELECT A.[State],  
     Split.a.value('.', 'VARCHAR(100)') AS String  
FROM  (SELECT [State],  
         CAST ('<M>' + REPLACE([City], ',', '</M><M>') + '</M>' AS XML) AS String  
     FROM  TableA) AS A CROSS APPLY String.nodes ('/M') AS Split(a);

这完全我想做的事情，但我想在 MySQL 中完成(正如您可以从图片中看到上述 SQL Server 查询的演示)

我坚信，当提供一种用某种语言做某事的方法时，按理说一定有一种方法可以撤消同样的事情。在 MySQL 中，您可以使用 GROUP_CONCAT 以一种方式透视数据，因此必须有一些方法来取消数据分组。

Answer 1

你可以用这样的查询来做到这一点

SELECT * FROM (
    SELECT `authorid`
        , TRIM(SUBSTRING_INDEX(emailaddress, ';', 1)) AS email
    FROM authors
UNION ALL
    SELECT `authorid`
        , TRIM(SUBSTRING_INDEX(SUBSTRING_INDEX(CONCAT(emailaddress,';;'), ';', 2),';',-1)) AS email
    FROM authors
UNION ALL
    SELECT `authorid`
        , TRIM(SUBSTRING_INDEX(SUBSTRING_INDEX(CONCAT(emailaddress,';;'), ';', 3),';',-1)) AS email
    FROM authors
) as emails
WHERE email is not null AND email <> '';

示例

mysql> SELECT * FROM authors;                                                                                                                                                                            +----+----------+-------------------------------------------+
| id | authorid | emailaddress                              |
+----+----------+-------------------------------------------+
|  1 |      123 | john@smith.com;sue@test.org               |
|  2 |     5271 | sally@john.doe                            |
|  3 |      834 | jacob@tom.smith;foo@bar.net; big@data.cow |
|  4 |       27 | tuesday@rubys.eat                         |
|  5 |     1977 | NULL                                      |
|  6 |      224 |                                           |
|  7 |       88 | miles@per.hour                            |
+----+----------+-------------------------------------------+
7 rows in set (0,00 sec)

mysql> SELECT * FROM (
    ->     SELECT `authorid`
    ->         , TRIM(SUBSTRING_INDEX(emailaddress, ';', 1)) AS email
    ->     FROM authors
    -> UNION ALL
    ->     SELECT `authorid`
    ->         , TRIM(SUBSTRING_INDEX(SUBSTRING_INDEX(CONCAT(emailaddress,';;'), ';', 2),';',-1)) AS email
    ->     FROM authors
    -> UNION ALL
    ->     SELECT `authorid`
    ->         , TRIM(SUBSTRING_INDEX(SUBSTRING_INDEX(CONCAT(emailaddress,';;'), ';', 3),';',-1)) AS email
    ->     FROM authors
    -> ) as emails
    -> WHERE email is not null AND email <> '';
+----------+-------------------+
| authorid | email             |
+----------+-------------------+
|      123 | john@smith.com    |
|     5271 | sally@john.doe    |
|      834 | jacob@tom.smith   |
|       27 | tuesday@rubys.eat |
|       88 | miles@per.hour    |
|      123 | sue@test.org      |
|      834 | foo@bar.net       |
|      834 | big@data.cow      |
+----------+-------------------+
8 rows in set (0,00 sec)

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