mysql 删除重复记录 保留一条

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-- 方法一
/**

错误码: 1093
You can't specify target table 'an' for update in FROM clause
用在select里的表,不能同时被修改
**/
DELETE an  FROM  t_anchor_cp an

WHERE an.c_order IN 
(

	SELECT t0.c_order FROM t_anchor_cp t0,(

	SELECT t1.c_foreign_id,t1.c_line_type_id,t1.c_anchor_no FROM t_anchor_cp t1 GROUP BY 
	t1.c_foreign_id,t1.c_line_type_id,t1.c_anchor_no HAVING COUNT(*)>1

	)t2

	WHERE t0.c_anchor_no = t2.c_anchor_no
	AND t0.c_foreign_id = t2.c_foreign_id
	AND t0.c_line_type_id = t2.c_line_type_id
	AND t0.c_order NOT IN 
	(
	SELECT MIN(c_order) FROM t_anchor_cp t1 GROUP BY 
	t1.c_foreign_id,t1.c_line_type_id,t1.c_anchor_no HAVING COUNT(*)>1

	)

)


-- 方法2 成功执行 使用临时表
DELETE an  FROM  t_anchor_cp an,(

	SELECT t0.c_order FROM t_anchor t0,(

	SELECT t1.c_foreign_id,t1.c_line_type_id,t1.c_anchor_no FROM t_anchor_cp t1 GROUP BY 
	t1.c_foreign_id,t1.c_line_type_id,t1.c_anchor_no HAVING COUNT(*)>1

	)t2

	WHERE t0.c_anchor_no = t2.c_anchor_no
	AND t0.c_foreign_id = t2.c_foreign_id
	AND t0.c_line_type_id = t2.c_line_type_id
	AND t0.c_order NOT IN 
	(
	SELECT MIN(c_order) FROM t_anchor_cp t1 GROUP BY 
	t1.c_foreign_id,t1.c_line_type_id,t1.c_anchor_no HAVING COUNT(*)>1

	)

)tt
WHERE tt.c_order = an.c_order


-- 方法三 创建临时表,用于查询,数据量少的话 
CREATE TABLE t_anchor_cp SELECT * FROM t_anchor

MySQL Error 1093 - Can't specify target table for update in FROM clause

引用

***************
*Cheekysoft:***
***************
In MySQL, you can't modify the same table which you use in the SELECT part.
Alternatively, try nesting the subquery deeper into a from clause ...

If you absolutely need the subquery, there's a workaround, but it's ugly for several reasons, including performance:

UPDATE tbl SET col = (
  SELECT ... FROM (SELECT.... FROM) AS x);

The nested subquery in the FROM clause creates an implicit temporary table, so it doesn't count as the same table you're updating.