MySQL 处理重复数据的方法(防止、删除)

CREATE TABLE person_tbl
(
 first_name CHAR(20),
 last_name CHAR(20),
 sex CHAR(10)
);

CREATE TABLE person_tbl
(
 first_name CHAR(20) NOT NULL,
 last_name CHAR(20) NOT NULL,
 sex CHAR(10),
 PRIMARY KEY (last_name, first_name)
);

mysql> INSERT IGNORE INTO person_tbl (last_name, first_name)
 -> VALUES( 'Jay', 'Thomas');
Query OK, 1 row affected (0.00 sec)
mysql> INSERT IGNORE INTO person_tbl (last_name, first_name)
 -> VALUES( 'Jay', 'Thomas');
Query OK, 0 rows affected (0.00 sec)

CREATE TABLE person_tbl
(
 first_name CHAR(20) NOT NULL,
 last_name CHAR(20) NOT NULL,
 sex CHAR(10),
 UNIQUE (last_name, first_name)
);

mysql> SELECT COUNT(*) as repetitions, last_name, first_name
 -> FROM person_tbl
 -> GROUP BY last_name, first_name
 -> HAVING repetitions > 1;

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

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

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;

mysql> ALTER IGNORE TABLE person_tbl
 -> ADD PRIMARY KEY (last_name, first_name);