如何使用两个内连接优化查询

Question

使用此查询来获取包含满足所有三个必需单词术语（联想、笔记本电脑、计算机）的单词的产品：

SELECT t1.id, t1.name, t1.price FROM
(SELECT p.id AS productid, name, price 
FROM products p JOIN productwords pw ON p.id = pw.productid 
JOIN words w ON pw.wordid = w.id WHERE word.term = 'lenovo') t1
INNER JOIN
(SELECT p.id AS productid, name, price
FROM products p JOIN productwords pw ON p.id = pw.productid 
JOIN words w ON pw.wordid = w.id WHERE word.term = 'laptop') t2
INNER JOIN
(SELECT p.id AS productid, name, price
FROM products p JOIN productwords pw ON p.id = pw.productid 
JOIN words w ON pw.wordid = w.id WHERE word.term = 'computer') t3
ON
t1.productid = t2.productid
AND
t1.productid = t3.productid
ORDER BY t1.name

据我所知，查询考虑了每个词的整个词表（表有索引。数据库是 MySql）。

查询能否以更好的方式重写，从而变得更快？ （表格包含数百万行）

例如对于子集，“laptop”搜索只考虑匹配“lenovo”的行 - 而“computer”搜索只考虑首先匹配“lenovo”然后是“laptop”的行。

谢谢！

Answer 1

您可以使用HAVING 子句：

SELECT p.id AS productid, name, price 
FROM products p
JOIN productwords pw ON p.id = pw.productid 
JOIN words w ON pw.wordid = w.id
WHERE word.term in ('lenovo','computer','laptop')
GROUP BY p.id , name, price 
HAVING COUNT(DISTINCT word.term) = 3

也就是说，如果我理解了这个问题，它看起来像 product -> words 是 1:n 关系，如果没有选择 word 表中的列，那应该可以正常工作。

Answer 2

这可能是一种更快的方法：

SELECT p.id, name, price FROM products p where EXISTS (select null from productwords pw1 JOIN words w1 ON pw1.wordid = w1.id where w1.term = 'lenovo' and p.id = pw1.productid ) and EXISTS (select null productwords pw2 JOIN words w2 ON pw2.wordid = w2.id where w2.term = 'laptop' and and p.id = pw2.productid ) and EXISTS (select null productwords pw3 ON p.id = pw3.productid JOIN words w3 where w3.term = 'computer' and p.id = pw3.productid )
ORDER BY name;