mysql多表联合查询操作实例分析_Mysql

本文实例讲述了mysql多表联合查询操作。分享给大家供大家参考，具体如下：

MySQL多表联合查询是MySQL数据库的一种查询方式，下面就为您介绍MySQL多表联合查询的语法，供您参考学习之用。

MySQL多表联合查询语法：

复制代码代码如下:

	SELECT * FROM 插入表 LEFT JOIN 主表 ON t1.lvid=t2.lv_id select * from mytable,title where 表名1.name=表名2.writer ;

mysql版本大于4.0，使用UNION进行查询，示例如下：

				?

									SELECT `id`, `name`, `date`, '' AS `type` FROM table_A WHERE 条件语句……

									 UNION

									SELECT `id`, `name`, `date`, '未完成' AS `type` FROM table_B WHERE 条件语句……

									 ORDER BY `id` LIMIT num;

mysql版本小于4.0，需要建立临时表，分为三步，示例如下：

第一步：建立临时表tmp_table_name并插入table_A中的相关记录

复制代码代码如下:

	$sql = "CREATE TEMPORARY TABLE tmp_table_name SELECT `id`, `name`, `date`, '完成' AS `type` FROM table_A WHERE 条件语句……";

第二步：从table_B中取得相关记录插入临时表tmp_table_name中

复制代码代码如下:

	INSERT INTO tmp_table_name SELECT `id`, `name`, `date2` AS `date`, '未完成' AS `type` FROM table_B WHERE 条件语句……

第三步：从临时表tmp_table_name中取出记录

				?

									SELECT * FROM tmp_table_name ORDER BY id DESC

union和order by、limit区别分析

代码示例:

				?

									CREATE TABLE `test1` (

									 `id` int(10) unsigned NOT NULL AUTO_INCREMENT,

									 `name` varchar(20) NOT NULL,

									 `desc` varchar(100) NOT NULL,

									 PRIMARY KEY (`id`)

									) ENGINE=InnoDB DEFAULT CHARSET=utf8

1. 以下查询会报错误：[Err] 1221 - Incorrect usage of UNION and ORDER BY

代码示例:

				?

									select * from test1 where name like 'A%' order by name

									union

									select * from test1 where name like 'B%' order by name

修改为：

代码示例:

				?

									select * from test1 where name like 'A%'

									union

									select * from test1 where name like 'B%' order by name

说明，在union中，不用括号的情况下，只能用一个order by(思考：union两边的order by的列名不一样时，会出现什么样的结果？),这会对union后的结果集进行排序。

修改为：

代码示例:

				?

									(select * from test1 where name like 'A%' order by name)

									union

									(select * from test1 where name like 'B%' order by name)

也是可以的，这两个order by在union前进行。

2. 同样

代码示例:

				?

									select * from test1 where name like 'A%' limit 10

									union

									select * from test1 where name like 'B%' limit 20

相当于：

代码示例:

				?

									(select * from test1 where name like 'A%' limit 10)

									union

									(select * from test1 where name like 'B%') limit 20

即后一个limit作用于的是union后的结果集，而不是union后的select。
也可以用括号括起来，以得到预期的结果：

3. UNION和UNION ALL区别

union会过滤掉union两边的select结果集中的重复的行，而union all不会过滤掉重复的行。

代码示例:

				?

									(select * from test1 where name like 'A%' limit 10)

									union

									(select * from test1 where name like 'B%' limit 20)

下面试一个年龄段分析的复杂sql语句

mysql多表联合查询操作实例分析

				?

									(

									 SELECT

									  '5~19' AS `age`,

									  SUM(`impression`) AS impression,

									  SUM(`click`) AS click,

									  sum(`cost`) AS cost

									 FROM

									  `adgroup_age_report`

									 WHERE

									  (

									   (

									    (`age` <= 19)

									    AND (`adgroup_id` = '61')

									   )

									   AND (`date` >= '2015-11-22')

									  )

									 AND (`date` <= '2017-02-20')

									)

									UNION

									 (

									  SELECT

									   '20~29' AS `age`,

									   SUM(`impression`) AS impression,

									   SUM(`click`) AS click,

									   sum(`cost`) AS cost

									  FROM

									   `adgroup_age_report`

									  WHERE

									   (

									    (

									     ((`age` <= 29) AND(`age` >= 20))

									     AND (`adgroup_id` = '61')

									    )

									    AND (`date` >= '2015-11-22')

									   )

									  AND (`date` <= '2017-02-20')

									 )

									UNION

									 (

									  SELECT

									   '30~39' AS `age`,

									   SUM(`impression`) AS impression,

									   SUM(`click`) AS click,

									   sum(`cost`) AS cost

									  FROM

									   `adgroup_age_report`

									  WHERE

									   (

									    (

									     ((`age` <= 39) AND(`age` >= 30))

									     AND (`adgroup_id` = '61')

									    )

									    AND (`date` >= '2015-11-22')

									   )

									  AND (`date` <= '2017-02-20')

									 )

									UNION

									 (

									  SELECT

									   '40~49' AS `age`,

									   SUM(`impression`) AS impression,

									   SUM(`click`) AS click,

									   sum(`cost`) AS cost

									  FROM

									   `adgroup_age_report`

									  WHERE

									   (

									    (

									     ((`age` <= 49) AND(`age` >= 40))

									     AND (`adgroup_id` = '61')

									    )

									    AND (`date` >= '2015-11-22')

									   )

									  AND (`date` <= '2017-02-20')

									 )

									UNION

									 (

									  SELECT

									   '50~59' AS `age`,

									   SUM(`impression`) AS impression,

									   SUM(`click`) AS click,

									   sum(`cost`) AS cost

									  FROM

									   `adgroup_age_report`

									  WHERE

									   (

									    (

									     ((`age` <= 59) AND(`age` >= 50))

									     AND (`adgroup_id` = '61')

									    )

									    AND (`date` >= '2015-11-22')

									   )

									  AND (`date` <= '2017-02-20')

									 )