mysql查询计数主表中第二表中具有多个属性的记录数

Question

我需要帮助构建 MYSQL 查询:

主表列出了待售车辆的姓名和地址。

属性(第二)表列出了车辆属性。

如何统计主表中属性表颜色为红色、年份为 2015 年、价格小于 15,000、客户地址为哥伦布的卖家数量？

select count(`master_id`)
from `customers` c
left join `attributes` a
on c.master_id = a.master_id
where (
a.name = 'color' and a.value = 'red' and 
a.name = 'year' and a.value = '2015' and 
a.name = 'price' and a.value > '15000' and 
c.city = 'Columbus';

Answer 1

您可以使用group by和having:

select count(*)
from (select master_id
      from `customers` c left join
           `attributes` a
           on c.master_id = a.master_id
      where (name, value) in ( ('color', 'red'), ('year', '2015'), ('price', '15000') and
            c.city = 'Columbus'
      group by a.master_id
      having count(distinct name) = 3
     ) x;

请注意，这使用元组来简化 where 子句。