Mysql基础第二十天,组合查询

1.创建组合查询

select vend_id,prod_id,prod_price from products where prod_price<=5;   //单价小于五的商品
     union
  select vend_id,prod_id,prod_price from products where vend_id in(1001,1002); // 商品id在10001,10002

2.union规则

3.包含或取消重复的行

包含重复的行

select vend_id,prod_id,prod_price from products where prod_price<=5;   //单价小于五的商品
     union  all
  select vend_id,prod_id,prod_price from products where vend_id in(1001,1002); // 商品id在10001,10002

取消重复的行

select vend_id,prod_id,prod_price from products where prod_price<=5;   //单价小于五的商品
     union
  select vend_id,prod_id,prod_price from products where vend_id in(1001,1002); // 商品id在10001,10002

4.对组合查询结果排序

select vend_id,prod_id,prod_price from products where prod_price<=5;   //单价小于五的商品
     union
  select vend_id,prod_id,prod_price from products where vend_id in(1001,1002) order by prod_price desc; // 商品id在10001,10002

注意order by只能在最后排序
感谢观看