sql 基础--mysql 5 (6)
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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 inset (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 inset (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 orderby pw_luck.uid; +-----+----------+------+-------+| uid | name | msg | price |+-----+----------+------+-------+|1| zhangsan |100|100||2| lisi |1001|1000||3| wang5 |1001|2000|+-----+----------+------+-------+3 rows inset (0.01 sec)
卡迪尔积: 无 where的行数是table1和table2行数的乘积
![技术分享](/upload/getfiles/default/2022/11/14/20221114015738462.jpg)
![技术分享](/upload/getfiles/default/2022/11/14/20221114015738487.jpg)
mysql>select pw_luck.uid,name,msg,price from pw_luck,pw_price orderby 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 inset (0.03 sec)
联结多个表 where语句用and 连接
原文:http://www.cnblogs.com/wjw334/p/4293108.html
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