mysql去重

原因：由于表是各地归集过来的，通过前置机数据交换，很多数据会重复。
目的：删除数据库某张表的重复数据

方法一(将查询出无重复的数据导入临时表，再将原表删除，再将临时表的数据导回原表) 适用于无主键，所有字段完全匹配，数据量小的情况：

DELIMITER //
CREATE PROCEDURE delete_rows(IN tablename VARCHAR(50))
BEGIN
SET @tablename = tablename;
SET @tmp_table = CONCAT(\'tmp_table_\',@tablename);

SET @create_table = CONCAT(\'DROP TABLE IF EXISTS \',@tmp_table);
PREPARE create_table FROM @create_table;
EXECUTE create_table;

SET @create_table = CONCAT(\'CREATE TEMPORARY TABLE \',@tmp_table,\' SELECT DISTINCT * from \',@tablename);
PREPARE create_table FROM @create_table;
EXECUTE create_table;

SET @create_table = CONCAT(\'TRUNCATE TABLE \',@tablename);
PREPARE create_table FROM @create_table;
EXECUTE create_table;

SET @create_table = CONCAT(\'INSERT INTO \',@tablename,\' SELECT * from \',@tmp_table);
PREPARE create_table FROM @create_table;
EXECUTE create_table;
END//
DELIMITER ;

CALL delete_rows(\'表名\');

方法二(给表加自增主键) 适用于根据某几个字段去重，有主键：

DELIMITER //
CREATE PROCEDURE delete_rows_1(IN tablename VARCHAR(50),IN fieldnames VARCHAR(100),IN autofield VARCHAR(50))
BEGIN
SET @tablename = tablename;
SET @fieldnames = fieldnames;
SET @autofield = autofield;

SET @create_table = CONCAT(\'DELETE FROM \', @tablename ,\' WHERE \', @autofield ,\' not in (SELECT id FROM (SELECT max(\', @autofield ,\') id FROM \', @tablename ,\' GROUP BY \', @fieldnames ,\') t)\');
PREPARE create_table FROM @create_table;
EXECUTE create_table;
END//
DELIMITER ;

CALL delete_rows_1(\'表名\', \'字段1,字段2,字段3...\', \'主键字段\');