删除表中多余的重复记录,根据单个字段判断,如字段名md5,重复记录只留有id最小的记录。
DELETE
FROM
ir_art
WHERE
md5 IN (
SELECT
md5
FROM
ir_art
GROUP BY
md5
HAVING
count(md5) > 1
)
AND id NOT IN (
SELECT
min(id)
FROM
ir_art
GROUP BY
md5
HAVING
count(md5) > 1
)
命令运行后出现“You can’t specify target table for update in FROM clause”
错误的意思是说,不能先select出同一表中的某些值,再update这个表(在同一语句中)。
将命令改为:
DELETE
FROM
ir_art
WHERE
md5 IN (
SELECT * FROM (
SELECT
md5
FROM
ir_art
GROUP BY
md5
HAVING
count(md5) > 1
)as tb
)
AND id NOT IN (
SELECT * FROM (
SELECT
min(id)
FROM
ir_art
GROUP BY
md5
HAVING
count(md5) > 1
)as tb
)
也就是说将select出的结果再通过中间表select一遍,这样就规避了错误。注意,这个问题只出现于mysql,mssql和oracle不会出现此问题。