本文介绍了MySQL:来自子查询的总和的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
是否可以对子查询中的两个值求和?
Is it possible to sum two values from subqueries?
我需要选择三个值:total_view、total_comments 和 rating.
I need select three values: total_view, total_comments and rating.
两个子查询都非常复杂，所以我不希望重复它.
Both subqueries is very complicated, so i don't wish duplicate it.
我的查询示例:
SELECT p.id,
(
FIRST subquery
) AS total_view,
(
SECOND subquery
) AS total_comments,
(
total_view * total_comments
) AS rating
FROM products p
WHERE p.status = "1"
ORDER BY rating DESC
推荐答案
我建议使用子查询:
SELECT p.*, (total_view * total_comments) as rating
FROM (SELECT p.id,
(FIRST subquery) AS total_view,
(SECOND subquery) AS total_comments,
FROM products p
WHERE p.status = '1' -- if status is a number, then remove quotes
) p
ORDER BY rating DESC;
MySQL 实现子查询.但是因为 ORDER BY 在计算列上，所以无论如何它都需要对数据进行排序，所以物化不是额外的开销.
MySQL materializes the subquery. But because the ORDER BY is on a computed column, it needs to sort the data anyway, so the materialization is not extra overhead.
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