mysql插入数据时，去掉重复的数据；

1. 利用insert ignore into语句去重

mysql> INSERT IGNORE INTO person_tbl (last_name, first_name)
    -> VALUES( 'J', 'T');
Query OK, 1 row affected (0.00 sec)
mysql> INSERT IGNORE INTO person_tbl (last_name, first_name)
    -> VALUES( 'J', 'T');
Query OK, 0 rows affected (0.00 sec)

2.查询过滤重复数据

①. 利用MySQL的关键字DISTINCT去重

mysql> SELECT DISTINCT last_name, first_name
    -> FROM person_tbl;

②. 利用group by进行去重

mysql> SELECT last_name, first_name
    -> FROM person_tbl
    -> GROUP BY (last_name, first_name);

3. 删除表中的重复数据

思路：先建一个临时表，把不重复的数据数据存放在临时表中，然后将原表删除，再将临时表rename成正式表

mysql> CREATE TABLE tmp SELECT last_name, first_name, sex FROM person_tbl  GROUP BY (last_name, first_name, sex);
mysql> DROP TABLE person_tbl;
mysql> ALTER TABLE tmp RENAME TO person_tbl;