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  • mysql学习(十)多表查询

    多表查询时,要给表名起别名,给字段名其别名(当两个表含有重复字段时)

    select p.name, c.name, pid from products p, cats c;//得到的结果为笛卡尔乘积

    1. select p.name as pname, p.price, p.desn, p.num from products p, cats c where c.id = p.cid ;//查询所有商品属于哪个分类
    2. select p.name as pname, p.price, p.desn, p.num from products p, cats c where c.id = p.cid and c.name like '%java%'//查询类名中含有java的商品信息
    3. mysql> select * from cats;
      +----+-----+-------+-----------+
      | id | pid | name | desn |
      +----+-----+-------+-----------+
      | 4 | 0 | soft | this soft |
      | 5 | 4 | java | this java |
      | 6 | 4 | php | this java |
      | 7 | 4 | c++ | this java |
      | 8 | 5 | j2ee | j2ee |
      | 9 | 5 | j2me | j2me |
      | 10 | 9 | j2me1 | j2me1 |
      +----+-----+-------+-----------+

    4. mysql> select a.id aid, a.name aname, b.id bid, b.name bname from cats a, cats b where a.pid = b.id;//查询所有分类
      +-----+-------+-----+-------+
      | aid | aname | bid | bname |
      +-----+-------+-----+-------+
      | 7 | c++ | 4 | soft |
      | 8 | j2ee | 5 | java |
      | 9 | j2me | 5 | java |
      | 10 | j2me1 | 9 | j2me |
      | 5 | java | 4 | soft |
      | 6 | php | 4 | soft |
      +-----+-------+-----+-------+
      6 rows in set (0.00 sec)

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  • 原文地址:https://www.cnblogs.com/zhoulikai/p/3361421.html
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