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12.子查询
子查询进行过滤
mysql> select msg from pw_luck where name = ‘wang5‘ -> ; +------+ | msg | +------+ | 1001 | | 1000 | | 1000 | | 100 | | 100 | +------+ 5 rows in set (0.03 sec) mysql> select uid from pw_luck where msg in (select msg from pw_luck where name = ‘wang5‘); +-----+ | uid | +-----+ | 0 | | 1 | | 2 | | 3 | | 7 | | 8 | | 9 | | 10 | | 12 | | 13 | | 14 | | 15 | +-----+ 12 rows in set (0.02 sec)
作为计算字段使用子查询 ,联表查询
mysql> select uid,price,(select count(*) from pw_luck where pw_luck.uid=pw_price.uid) as pw_luck_cou nt from pw_price order by uid; +-----+-------+---------------+ | uid | price | pw_luck_count | +-----+-------+---------------+ | 1 | 100 | 1 | | 2 | 1000 | 1 | | 3 | 2000 | 1 | +-----+-------+---------------+ 3 rows in set (0.02 sec)
13联结表
外键：某个表中的一列，他包含另一个表中的主键值，定义了两表之间的关系。
mysql> select pw_luck.uid,name,msg,price from pw_luck,pw_price where pw_luck.uid=pw_price.uid order by pw_luck.uid; +-----+----------+------+-------+ | uid | name | msg | price | +-----+----------+------+-------+ | 1 | zhangsan | 100 | 100 | | 2 | lisi | 1001 | 1000 | | 3 | wang5 | 1001 | 2000 | +-----+----------+------+-------+ 3 rows in set (0.01 sec)
卡迪尔积： 无 where的行数是table1和table2行数的乘积
mysql> select pw_luck.uid,name,msg,price from pw_luck,pw_price order by pw_luck.uid; +-----+-----------+------+-------+ | uid | name | msg | price | +-----+-----------+------+-------+ | 0 | Wilson | 100 | 100 | | 0 | Wilson | 100 | 1000 | | 0 | Wilson | 100 | 2000 | | 1 | zhangsan | 100 | 2000 | | 1 | zhangsan | 100 | 100 | | 1 | zhangsan | 100 | 1000 | | 2 | lisi | 1001 | 2000 | | 2 | lisi | 1001 | 100 | | 2 | lisi | 1001 | 1000 | | 3 | wang5 | 1001 | 1000 | | 3 | wang5 | 1001 | 2000 | | 3 | wang5 | 1001 | 100 | | 7 | zhangsan7 | 1000 | 100 | | 7 | zhangsan7 | 1000 | 1000 | | 7 | zhangsan7 | 1000 | 2000 | | 8 | zhangsan8 | 1000 | 2000 | | 8 | zhangsan8 | 1000 | 100 | | 8 | zhangsan8 | 1000 | 1000 | | 9 | zhangsan9 | 1000 | 2000 | | 9 | zhangsan9 | 1000 | 100 | | 9 | zhangsan9 | 1000 | 1000 | | 10 | wang5 | 1000 | 1000 | | 10 | wang5 | 1000 | 2000 | | 10 | wang5 | 1000 | 100 | | 11 | wang5% | 2000 | 1000 | | 11 | wang5% | 2000 | 2000 | | 11 | wang5% | 2000 | 100 | | 12 | WANG5 | 1000 | 100 | | 12 | WANG5 | 1000 | 1000 | | 12 | WANG5 | 1000 | 2000 | | 13 | wang5 | 100 | 2000 | | 13 | wang5 | 100 | 100 | | 13 | wang5 | 100 | 1000 | | 14 | wang5 | 100 | 2000 | | 14 | wang5 | 100 | 100 | | 14 | wang5 | 100 | 1000 | | 15 | zhangsan7 | 1000 | 1000 | | 15 | zhangsan7 | 1000 | 2000 | | 15 | zhangsan7 | 1000 | 100 | | 16 | zhangsan7 | 1002 | 1000 | | 16 | zhangsan7 | 1002 | 2000 | | 16 | zhangsan7 | 1002 | 100 | | 17 | zhangsan7 | 1002 | 2000 | | 17 | zhangsan7 | 1002 | 100 | | 17 | zhangsan7 | 1002 | 1000 | +-----+-----------+------+-------+ 45 rows in set (0.03 sec)
联结多个表 where语句用and 连接
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原文地址：http://www.cnblogs.com/wjw334/p/4293108.html
