mysql 查询删除重复数据，保留其中一条数据

一、查询重复数据 --------根据多个字段查询重复数据

SELECT
    *
FROM
    table_name a
WHERE
    (a.字段1, a.字段2) IN (
        SELECT
            字段1,
            字段2
        FROM
            table_name 
        GROUP BY
            字段1,
            字段2
        HAVING
            count(*) > 1
    )

二、根据多个字段删除重复数据，只保留一条数据 注意：这种写法 必须保证有一个主键 如id，删除多余数据是 ，是根据id，保留最小或者最大的一条数据

DELETE
FROM
	table_name 
WHERE
	(字段1, 字段2) IN (
		SELECT
			t.字段1,
			t.字段2
		FROM
			(
				SELECT
					字段1,
					字段2
				FROM
					table_name 
				GROUP BY
					字段1,
					字段2
				HAVING
					count(1) > 1
			) t
	)
AND id NOT IN (
	SELECT
		dt.id
	FROM
		(
			SELECT
				min(id) AS id
			FROM
				table_name 
			GROUP BY
				字段1,
				字段2
			HAVING
				count(1) > 1
		) dt
)

三、没有主键时删除重复数据

###字段1,字段2,字段3,字段4,字段5,字段6 是表中所有字段
create table new_table_temp
select DISTINCT 字段1,字段2,字段3,字段4,字段5,字段6 from table_name

delete from table_name
insert into table_name
select * from new_table_temp

DROP TABLE new_table_temp