Question

我有一个数据库，人们可以通过命令发送信息并将其存储在数据库中。同一个人每天可以有许多报告，下一个查询仅显示最新的报告：

SELECT
    r1.id,
    r1.nickname,
    r1.fecha,
    r1.bestia1,
    r1.bestia2,
    r1.bestia3,
    r1.bestia4,
    r1.bestia5
FROM
    reporte AS r1
INNER JOIN
    ( SELECT
          nickname,
          MAX(fecha) AS max_date
      FROM
          reporte
      GROUP BY
          nickname ) AS latests_reports ON latests_reports.nickname = r1.nickname AND latests_reports.max_date = r1.fecha
ORDER BY
    r1.fecha DESC

但是现在我想删除除上一个查询返回的记录以外的所有记录，该怎么办？

Answer 1

编辑：我已将查询从EXITS()更新为NOT EXISTS() 您要删除所有记录，但查询中列出的记录除外。这是您的查询：：

DELETE FROM Reporte WHERE NOT EXISTS 
        (
            SELECT 1 FROM
            (
                SELECT r1.id, 
                FROM reporte AS r1 
                INNER JOIN ( SELECT nickname, MAX(fecha) AS max_date  FROM reporte GROUP BY nickname ) AS latests_reports  
                    ON latests_reports.nickname =  r1.nickname 
                    AND latests_reports.max_date = r1.fecha 
            ) r WHERE Reporte.Id= r.Id
        )

Answer 2

理想情况下，您会按照一组步骤进行操作，但是可以通过以下方法将其单步执行：

DELETE FROM reporte
WHERE id not in
(
  SELECT a.id FROM(
    SELECT r1.id
    FROM reporte AS r1 
    INNER JOIN ( SELECT nickname, MAX(fecha) AS max_date 
    FROM reporte GROUP BY nickname ) AS latests_reports 
    ON latests_reports.nickname = 
    r1.nickname AND latests_reports.max_date = r1.fecha 
  ) a
)

您需要在其中使用a.id查询，否则MySQL会抱怨它无法更新reporte表

作为单独的步骤：

    CREATE TABLE to_keep AS
    SELECT r1.id
    FROM reporte AS r1 
    INNER JOIN 
    ( SELECT nickname, MAX(fecha) AS max_date FROM reporte GROUP BY nickname ) AS latests_reports 
    ON 
      latests_reports.nickname = r1.nickname AND 
      latests_reports.max_date = r1.fecha

    DELETE r.* FROM reporte r LEFT JOIN to_keep k ON r.id = k.id WHERE k.id IS NULL

    DROP TABLE to_keep

从数据库中删除，但该过滤器除外

2 个答案: