标签：mysql
ANY和SOME子查询
Any和some关键字是同义词，表示满足其中任一条件。
通过创建表达式，对返回的结果进行比较，并输出符合条件的结果。
mysql> select * from t2;
+------+-------+------+
| id | name | age |
+------+-------+------+
| 1 | Mark | 29 |
| 2 | Frank | 32 |
| 3 | Niko | 27 |
+------+-------+------+
3 rows in set (0.00 sec)
mysql> select * from t1;
+------+-------+------+
| id | name | age |
+------+-------+------+
| 1 | Tube | 31 |
| 2 | Kevin | 34 |
| 3 | Todd | 32 |
+------+-------+------+
3 rows in set (0.00 sec)
mysql> select * from t2 where age >any (select age from t1);
+------+-------+------+
| id | name | age |
+------+-------+------+
| 2 | Frank | 32 |
+------+-------+------+
1 row in set (0.07 sec)
EXITS和NOT EXITS子查询
EXITS和NOT EXITS可以说是一种判断子查询。
系统对子查询进行运算，并判断是否有返回行。如果有则执行外层语句中的查询，如果没有则不进行查询。
mysql> select * from log;
+------+----------+------------------------------------------------+
| id | category | log |
+------+----------+------------------------------------------------+
| 1 | Nginx | upstream timed out(110: Connection timed out) |
| 2 | Apache | File does notexist:/var/www/html/1.html |
| 3 | Apache | Could not openfile:/var/images/banner.gif |
| 4 | MySQL | InnoDB: Unable tolock ./ibdata1, error: 11 |
+------+----------+------------------------------------------------+
4 rows in set (0.05 sec)
mysql>
mysql>
mysql> select * from state;
+---------+-------+---------+---------+
| apache | Nginx | App | MySQL |
+---------+-------+---------+---------+
| Succeed | Fail | Succeed | Succeed |
+---------+-------+---------+---------+
1 row in set (0.09 sec)
mysql> select * from log where category= ‘Nginx‘ and exists (select * from state where Nginx=‘Fail‘);
+------+----------+------------------------------------------------+
| id | category | log |
+------+----------+------------------------------------------------+
| 1 | Nginx | upstream timed out(110: Connection timed out) |
+------+----------+------------------------------------------------+
1 row in set (0.00 sec)
如果查询结果为真，显示；为假不显示。
mysql> select * from log where category= ‘Apache‘;
+------+----------+--------------------------------------------+
| id | category | log |
+------+----------+--------------------------------------------+
| 2 | Apache | File does notexist:/var/www/html/1.html |
| 3 | Apache | Could not openfile:/var/images/banner.gif |
+------+----------+--------------------------------------------+
2 rows in set (0.00 sec)
mysql> select * from log where category= ‘Apache‘ and exists (select * from state where apache=‘Fail‘);
Empty set (0.00 sec)
IN子查询
IN关键字对子查询结果进行运算，并判断是否返回行。如果有则执行外部查询语句。如果没有则不执行。
外查询返回的结果匹配子查询的结果。
mysql> select * from People;
+------+------+-----------+-------------+
| name | age | certnum | phone |
+------+------+-----------+-------------+
| Lee | 20 | 123456789 | 13021981234 |
| John | 32 | 987654321 | 13998763456 |
| Lucy | 45 | 678954321 | 13098784321 |
| Ken | 33 | 986745321 | 18609073544 |
+------+------+-----------+-------------+
4 rows in set (0.03 sec)
mysql> select * from Blacklist;
+------+------+-------+--------+
| ID | Name | Price | Level |
+------+------+-------+--------+
| 1 | John | 3000 | normal |
| 2 | Lucy | 24000 | hard |
+------+------+-------+--------+
2 rows in set (0.08 sec)
mysql> select * from People where nameIN
-> (select Name from Blacklist);
+------+------+-----------+-------------+
| name | age | certnum | phone |
+------+------+-----------+-------------+
| John | 32 | 987654321 | 13998763456 |
| Lucy | 45 | 678954321 | 13098784321 |
+------+------+-----------+-------------+
2 rows in set (0.00 sec)
IN子查询适合从大的结果集拾取指定条件的小的结果集。这个小的结果集同时也是另外一个表中的内容。
Union子查询 （唯一性）
Union用于合并查询结果。可以将多条select语句查询的结果组合成单个结果集。
列数必须相同，使用ALL关键字则拼接两张表。
mysql> select * from People;
+------+------+-----------+-------------+
| name | age | certnum | phone |
+------+------+-----------+-------------+
| Lee | 20 | 123456789 | 13021981234 |
| John | 32 | 987654321 | 13998763456 |
| Lucy | 45 | 678954321 | 13098784321 |
| Ken | 33 | 986745321 | 18609073544 |
+------+------+-----------+-------------+
4 rows in set (0.00 sec)
mysql> create table People2 like People;
Query OK, 0 rows affected (0.04 sec)
mysql> insert into People2 select * from People where age=45;
Query OK, 1 row affected (0.02 sec)
Records: 1 Duplicates: 0 Warnings: 0
mysql> select * from People2;
+------+------+-----------+-------------+
| name | age | certnum | phone |
+------+------+-----------+-------------+
| Lucy | 45 | 678954321 | 13098784321 |
+------+------+-----------+-------------+
1 row in set (0.00 sec)
mysql> insert into People2 values(‘jingjing‘,31,123321456,18812344321);
Query OK, 1 row affected (0.01 sec)
mysql> select * from People;
+------+------+-----------+-------------+
| name | age | certnum | phone |
+------+------+-----------+-------------+
| lee | 20 | 123456789 | 13021981234 |
| John | 32 | 987654321 | 13998763456 |
| Lucy | 45 | 678954321 | 13098784321 |
| Ken | 33 | 986745321 | 18609073544 |
+------+------+-----------+-------------+
4 rows in set (0.00 sec)
mysql> select * from People2;
+----------+------+-----------+-------------+
| name | age | certnum | phone |
+----------+------+-----------+-------------+
| Lucy | 45 | 678954321 | 13098784321 |
| jingjing | 31 | 123321456 | 18812344321 |
+----------+------+-----------+-------------+
2 rows in set (0.00 sec)
mysql> select * from People union select* from People2;
+----------+------+-----------+-------------+
| name | age | certnum | phone |
+----------+------+-----------+-------------+
| lee | 20 | 123456789 | 13021981234 |
| John | 32 | 987654321 | 13998763456 |
| Lucy | 45 | 678954321 | 13098784321 |
| Ken | 33 | 986745321 | 18609073544 |
| jingjing | 31 | 123321456 | 18812344321 |
+----------+------+-----------+-------------+
5 rows in set (0.00 sec)
重复的一条数据不存在了。
mysql> select * from People union allselect * from People2;
+----------+------+-----------+-------------+
| name | age | certnum | phone |
+----------+------+-----------+-------------+
| lee | 20 | 123456789 | 13021981234 |
| John | 32 | 987654321 | 13998763456 |
| Lucy | 45 | 678954321 | 13098784321 |
| Ken | 33 | 986745321 | 18609073544 |
| Lucy | 45 | 678954321 | 13098784321 |
| jingjing | 31 | 123321456 | 18812344321 |
+----------+------+-----------+-------------+
6 rows in set (0.00 sec)
简单的拼接
mysql> select * from Blacklist;
+------+------+-------+--------+
| ID | Name | Price | Level |
+------+------+-------+--------+
| 1 | John | 3000 | normal |
| 2 | Lucy | 24000 | hard |
+------+------+-------+--------+
2 rows in set (0.00 sec)
mysql> select * from People2;
+----------+------+-----------+-------------+
| name | age | certnum | phone |
+----------+------+-----------+-------------+
| Lucy | 45 | 678954321 | 13098784321 |
| jingjing | 31 | 123321456 | 18812344321 |
+----------+------+-----------+-------------+
2 rows in set (0.00 sec)
当列数据类型不一样的时候
mysql> select * from Blacklist unionselect * from People2;
+----------+------+-----------+-------------+
| ID | Name | Price | Level |
+----------+------+-----------+-------------+
| 1 | John | 3000 | normal |
| 2 | Lucy | 24000 | hard |
| Lucy | 45 | 678954321 | 13098784321 |
| jingjing | 31 | 123321456 | 18812344321 |
+----------+------+-----------+-------------+
4 rows in set (0.00 sec)
mysql> select * from Blacklist union allselect * from People2;
+----------+------+-----------+-------------+
| ID | Name | Price | Level |
+----------+------+-----------+-------------+
| 1 | John | 3000 | normal |
| 2 | Lucy | 24000 | hard |
| Lucy | 45 | 678954321 | 13098784321 |
| jingjing | 31 | 123321456 | 18812344321 |
+----------+------+-----------+-------------+
4 rows in set (0.00 sec)
加不加ALL一样
mysql> select name,price from Blacklistunion all select name,certnum from People2;
+----------+-----------+
| name | price |
+----------+-----------+
| John | 3000 |
| Lucy | 24000 |
| Lucy | 678954321 |
| jingjing | 123321456 |
+----------+-----------+
4 rows in set (0.00 sec)
mysql> select name,price from Blacklistunion select name,certnum from People2;
+----------+-----------+
| name | price |
+----------+-----------+
| John | 3000 |
| Lucy | 24000 |
| Lucy | 678954321 |
| jingjing | 123321456 |
+----------+-----------+
4 rows in set (0.00 sec)
mysql> update People2 set certnum=24000where name=‘Lucy‘;
Query OK, 1 row affected (0.02 sec)
Rows matched: 1 Changed: 1 Warnings: 0
mysql> select name,certnum from People2where name=‘Lucy‘;
+------+---------+
| name | certnum |
+------+---------+
| Lucy | 24000 |
+------+---------+
1 row in set (0.00 sec)
mysql> select name,price from Blacklistunion select name,certnum from People2;
+----------+-----------+
| name | price |
+----------+-----------+
| John | 3000 |
| Lucy | 24000 |
| jingjing | 123321456 |
+----------+-----------+
3 rows in set (0.00 sec)
mysql> select name,price from Blacklistunion all select name,certnum from People2;
+----------+-----------+
| name | price |
+----------+-----------+
| John | 3000 |
| Lucy | 24000 |
| Lucy | 24000 |
| jingjing | 123321456 |
+----------+-----------+
4 rows in set (0.00 sec)
能不能去重：取决于列数据类型一样，数据一样。
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标签：mysql
原文地址：http://sunshinesnail.blog.51cto.com/1179761/1736539
