mysql - 根据列的最小值选择记录，但保留其他约束

Question

cont 表包含许多具有相同userid 的记录。我试图从 dist 列中为每个唯一的用户 ID 选择最小距离值。

SELECT sec.*, r.contid, r.lng, r.lat, **math formula for distance** < $withinMiles AS dist
FROM cont r
JOIN s_cont s
ON r.userid = s.userid
WHERE (( **math formula for distance**))
ORDER BY dist ASC

Answer 1

您需要使用带有having子句的分组:

SELECT sec.*, r.contid, r.lng, r.lat, MIN(**math formula for distance**) AS dist
FROM cont r
JOIN s_cont s
ON r.userid = s.userid
GROUP BY r.userid
HAVING MIN(**math formula for distance**) < $withinMiles
ORDER BY dist ASC

GROUP BY 会将具有相同用户 ID 的行分组在一起，MIN() 将从这些行中提取最小值(即具有相同用户 ID 的行)。 HAVING 的工作方式与 WHERE 类似，但基于已聚合的值。