mysql - 如何在mysql中使用MAX来获得以下结果

Question

这是查询

SELECT research_id,
    IF(product_id = 4, IF(value REGEXP '^-?[0-9]+$' > 0, value, IF(value = 'Yes', 1, 0)), 0) AS val1,
    IF(product_id = 8, IF(value REGEXP '^-?[0-9]+$' > 0, value, IF(value = 'Yes', 1, 0)), 0) AS val2
FROM research_product_details rpd
LEFT JOIN products p
ON rpd.product_id = p.id
WHERE (product_id = 4 AND value >= 50) OR (product_id = 8 AND value >= 50)
ORDER BY research_id ASC , product_id ASC

我从这个查询中得到了这个结果

我想要像关注

Answer 1

正如 @Jkike 在他的评论中提到的，实现您想要的效果的一种方法是简单地包装当前查询和 GROUP BY research_id 列，选择最大值对于 val1 和 val2 列:

SELECT t.research_id AS research_id, MAX(t.val1) AS val1, MAX(t.val2) AS val2
FROM
(
    SELECT research_id,
        IF(product_id = 4, IF(value REGEXP '^-?[0-9]+$' > 0, value, IF(value = 'Yes', 1, 0)), 0) AS val1,
        IF(product_id = 8, IF(value REGEXP '^-?[0-9]+$' > 0, value, IF(value = 'Yes', 1, 0)), 0) AS val2
    FROM research_product_details rpd
    LEFT JOIN products p
    ON rpd.product_id = p.id
    WHERE (product_id = 4 AND value >= 50) OR (product_id = 8 AND value >= 50)
    ORDER BY research_id ASC , product_id ASC
) AS t
GROUP BY t.research_id