SQL

2024-07-16 13:34| 来源: 网络整理| 查看: 265

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;

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