本文例項講述了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資料庫的一種查詢方式，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：
複製程式碼 程式碼如下: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版本大於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`,'未完成' AS `type` FROM table_B WHERE 條件語句……
 ORDER BY `id` LIMIT num;

mysql版本小於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並插入table_A中的相關記錄
複製程式碼 程式碼如下:$sql = "CREATE TEMPORARY TABLE tmp_table_name SELECT `id`,'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
複製程式碼 程式碼如下:INSERT INTO tmp_table_name SELECT `id`,`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

程式碼示例:

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

程式碼示例:

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

修改為：

程式碼示例:

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，會出現什麼樣的結果？),這會對union後的結果集進行排序。

修改為：

程式碼示例:

(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

程式碼示例:

select * from test1 where name like 'A%' limit 10
union
select * from test1 where name like 'B%' limit 20

相當於：

程式碼示例:

(select * from test1 where name like 'A%' limit 10)
union
(select * from test1 where name like 'B%') limit 20

即後一個limit作用於的是union後的結果集，而不是union後的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結果集中的重複的行，而union all不會過濾掉重複的行。

程式碼示例:

(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複雜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(`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(`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(`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(`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')
 )

更多關於MySQL相關內容感興趣的讀者可檢視本站專題：《MySQL查詢技巧大全》、《MySQL常用函式大彙總》、《MySQL日誌操作技巧大全》、《MySQL事務操作技巧彙總》、《MySQL儲存過程技巧大全》及《MySQL資料庫鎖相關技巧彙總》

希望本文所述對大家MySQL資料庫計有所幫助。