删除重复行
DELETE FROM ecm_member_login_session
WHERE (number , client_code) IN (
SELECT number, client_code FROM mall.ecm_member_login_session GROUP BY number , client_code HAVING COUNT(*) > 1)
AND update_time NOT IN (
SELECT MAX(update_time) FROM mall.ecm_member_login_session GROUP BY number , client_code HAVING COUNT(*) > 1);
但是报1093错误
14:57:04 DELETE FROM ecm_member_login_session WHERE (number , client_code) IN ( SELECT number, client_code FROM mall.ecm_member_login_session GROUP BY number , client_code HAVING COUNT(*) > 1) AND update_time NOT IN ( SELECT MAX(update_time) FROM mall.ecm_member_login_session GROUP BY number , client_code HAVING COUNT(*) > 1) Error Code: 1093. You can't specify target table 'ecm_member_login_session' for update in FROM clause 0.046 sec
后来在 嵌套查询语句里面再嵌套一层即可， 是因为mysql限制update（包括delete）操作表名与嵌套子查询语句里的表名一样的原因。
语句改为如下
DELETE FROM ecm_member_login_session
WHERE (number , client_code) IN (
SELECT number, client_code from (SELECT number, client_code FROM ecm_member_login_session GROUP BY number , client_code HAVING COUNT(*) > 1) A)
AND update_time NOT IN (
SELECT update_time from (SELECT MAX(update_time) FROM ecm_member_login_session GROUP BY number , client_code HAVING COUNT(*) > 1) A);
mysql文档：
上面是目前MYSQL5.0仍然有的限制，文档中说： In general, you cannot modify a table and select from the same table in a subquery. For example, this limitation applies to statements of the following forms: DELETE FROM t WHERE ... (SELECT ... FROM t ...);UPDATE t ... WHERE col = (SELECT ... FROM t ...);{INSERT|REPLACE} INTO t (SELECT ... FROM t ...); Exception: The preceding prohibition does not apply if you are using a subquery for the modified table in the FROM clause. Example: UPDATE t ... WHERE col = (SELECT (SELECT ... FROM t...) AS _t ...); Here the prohibition does not apply because a subquery in the FROM clause is materialized as a temporary table, so the relevant rows in t have already been selected by the time the update to t takes place.
参考：
http://blog.163.com/xiaoqiu_1120/blog/static/121632322007112411424982/
