有时需要以某一字段作为分组,筛选每一组的另一字段值最大(或最小)的记录。例如,有如下表 app,存储了 app 的 ID、名称、版本号等信息。现在要筛选出每个 app 版本最大的记录。
方法一
SELECT a.* FROM app a
WHERE a.app_version = (SELECT MAX(b.app_version) FROM app b WHERE b.app_name = a.app_name)
ORDER BY a.app_name;
方法二
SELECT a.* FROM app a
WHERE NOT EXISTS(SELECT 1 FROM app b WHERE b.app_name = a.app_name AND b.app_version > a.app_version)
ORDER BY a.app_name;
方法三
SELECT a.*
FROM app a, (SELECT app_name, MAX(app_version) AS app_version FROM app GROUP BY app_name) b
WHERE a.app_name = b.app_name
AND a.app_version = b.app_version
ORDER BY a.app_name;
方法四
SELECT a.*
FROM app a INNER JOIN (SELECT app_name, MAX(app_version) AS app_version FROM app GROUP BY app_name) b
ON a.app_name = b.app_name
AND a.app_version = b.app_version
ORDER BY a.app_name;