本文實例講述了mysql多表聯合查詢操作。分享給大家供大家參考，具體如下：
MySQL多表聯合查詢是MySQL數據庫的一種查詢方式，下面就為您介紹MySQL多表聯合查詢的語法，供您參考學習之用。
MySQL多表聯合查詢語法：
復制代碼 代碼如下:
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進行查詢，示例如下：
SELECT `id`, `name`, `date`, '' AS `type` FROM table_A WHERE 條件語句……
UNION
SELECT `id`, `name`, `date`, '未完成' AS `type` FROM table_B WHERE 條件語句……
ORDER BY `id` LIMIT num;
mysql版本小于4.0，需要建立臨時表，分為三步，示例如下：
第一步：建立臨時表tmp_table_name并插入table_A中的相關記錄
復制代碼 代碼如下:
$sql = "CREATE TEMPORARY TABLE tmp_table_name SELECT `id`, `name`, `date`, '完成' AS `type` FROM table_A WHERE 條件語句……";
第二步：從table_B中取得相關記錄插入臨時表tmp_table_name中
復制代碼 代碼如下:
INSERT INTO tmp_table_name SELECT `id`, `name`, `date2` AS `date`, '未完成' AS `type` FROM table_B WHERE 條件語句……
第三步：從臨時表tmp_table_name中取出記錄
SELECT * FROM tmp_table_name ORDER BY id DESC
union和order by、limit區別分析
代碼示例:
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. 以下查詢會報錯誤：[Err] 1221 - Incorrect usage of UNION and ORDER BY
代碼示例:
select * from test1 where name like 'A%' order by name
union
select * from test1 where name like 'B%' order by name
修改為：
代碼示例:
select * from test1 where name like 'A%'
union
select * from test1 where name like 'B%' order by name
說明，在union中，不用括號的情況下，只能用一個order by(思考：union兩邊的order by的列名不一樣時，會出現什么樣的結果？),這會對union后的結果集進行排序。
修改為：
代碼示例:
(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，這兩個order by在union前進行。
2. 同樣
代碼示例:
select * from test1 where name like 'A%' limit 10
union
select * from test1 where name like 'B%' limit 20
相當于：
代碼示例:
(select * from test1 where name like 'A%' limit 10)
union
(select * from test1 where name like 'B%') limit 20
即后一個limit作用于的是union后的結果集，而不是union后的select。
也可以用括號括起來，以得到預期的結果：
3. UNION和UNION ALL區別
union會過濾掉union兩邊的select結果集中的重復的行，而union all不會過濾掉重復的行。
代碼示例:
(select * from test1 where name like 'A%' limit 10)
union
(select * from test1 where name like 'B%' limit 20)
下面試一個年齡段分析的復雜sql語句
(
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')
)
更多關于MySQL相關內容感興趣的讀者可查看本站專題：《MySQL查詢技巧大全》、《MySQL常用函數大匯總》、《MySQL日志操作技巧大全》、《MySQL事務操作技巧匯總》、《MySQL存儲過程技巧大全》及《MySQL數據庫鎖相關技巧匯總》
希望本文所述對大家MySQL數據庫計有所幫助。
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