MySQL 返回更新值（RETURNING），mysqlreturning

MySQL 返回更新值（RETURNING），mysqlreturning
在寫SQL中，經常會有諸如更新了一行記錄，之後要擷取更新過的這一行。 本身從程式來說，沒啥難度，大不了把這行緩衝起來，完了直接存取。 但是從資料庫的角度出發，怎麼能快速的拿出來，而又不對原表進行二次掃描？ 比如其他資料庫提供了如下的文法來實現：


返回更新掉的行：

t_girl=# update t1 set log_time = now() where id in (1,2,3) returning *; id |          log_time          ----+----------------------------  1 | 2014-11-26 11:06:53.555217  2 | 2014-11-26 11:06:53.555217  3 | 2014-11-26 11:06:53.555217(3 rows)UPDATE 3Time: 6.991 ms

返回刪除掉的行：

t_girl=# delete from t1 where id < 2 returning *; id |          log_time          ----+----------------------------  1 | 2014-11-26 11:06:53.555217(1 row)DELETE 1Time: 6.042 ms

返回插入後的行：

t_girl=# insert into t1 select 1,now() returning *; id |          log_time          ----+----------------------------  1 | 2014-11-26 11:07:40.431766(1 row)INSERT 0 1Time: 6.107 mst_girl=# 

那在MySQL裡如何?呢？ 
我可以建立幾張記憶體表來來儲存這些傳回值，如下：

CREATE TABLE t1_insert ENGINE MEMORY SELECT * FROM  t1 WHERE FALSE;CREATE TABLE t1_update ENGINE MEMORY SELECT * FROM  t1 WHERE FALSE;CREATE TABLE t1_delete ENGINE MEMORY SELECT * FROM  t1 WHERE FALSE;ALTER TABLE t1_insert ADD PRIMARY KEY (id);ALTER TABLE t1_update ADD PRIMARY KEY (id);ALTER TABLE t1_delete ADD PRIMARY KEY (id);

以上建立了三張表來存放對應的操作。 t1_insert 儲存插入；t1_update 儲存更新；t1_delete 儲存刪除。


那這樣的話，我來建立對應的觸發器完成。

DELIMITER $$USE `t_girl`$$DROP TRIGGER /*!50032 IF EXISTS */ `tr_t1_insert_after`$$CREATE    /*!50017 DEFINER = 'root'@'localhost' */    TRIGGER `tr_t1_insert_after` AFTER INSERT ON `t1`     FOR EACH ROW BEGIN      REPLACE INTO t1_insert VALUES (new.id,new.log_time);    END;$$DELIMITER ;DELIMITER $$USE `t_girl`$$DROP TRIGGER /*!50032 IF EXISTS */ `tr_t1_update_after`$$CREATE    /*!50017 DEFINER = 'root'@'localhost' */    TRIGGER `tr_t1_update_after` AFTER UPDATE ON `t1`     FOR EACH ROW BEGIN      REPLACE INTO t1_update VALUES (new.id,new.log_time);    END;$$DELIMITER ;DELIMITER $$USE `t_girl`$$DROP TRIGGER /*!50032 IF EXISTS */ `tr_t1_delete_after`$$CREATE    /*!50017 DEFINER = 'root'@'localhost' */    TRIGGER `tr_t1_delete_after` AFTER DELETE ON `t1`     FOR EACH ROW BEGIN      REPLACE INTO t1_delete VALUES (old.id,old.log_time);；    END;$$DELIMITER ;

建立好了以上的表和觸發器後， 拿到傳回值就非常容易了， 我直接從以上幾張表來查詢就是。


我現在來示範：
更新：

mysql> truncate table t1_update;Query OK, 0 rows affected (0.00 sec)mysql> UPDATE t1 SET log_time = NOW() WHERE id < 15;Query OK, 3 rows affected (0.01 sec)Rows matched: 3  Changed: 3  Warnings: 0

擷取更新記錄：

mysql> select * from t1_update;+----+----------------------------+| id | log_time                   |+----+----------------------------+| 12 | 2014-11-26 13:38:06.000000 || 13 | 2014-11-26 13:38:06.000000 || 14 | 2014-11-26 13:38:06.000000 |+----+----------------------------+3 rows in set (0.00 sec)

插入：

mysql> truncate table t1_insert;Query OK, 0 rows affected (0.00 sec)mysql> INSERT INTO t1 VALUES (1,NOW());Query OK, 1 row affected (0.08 sec)

擷取插入記錄：

mysql> select * from t1_insert;+----+----------------------------+| id | log_time                   |+----+----------------------------+|  1 | 2014-11-26 13:38:06.000000 |+----+----------------------------+1 row in set (0.00 sec)

刪除：

mysql> truncate table t1_delete;Query OK, 0 rows affected (0.00 sec)mysql> DELETE FROM t1 WHERE id < 15;Query OK, 4 rows affected (0.01 sec)

擷取刪除記錄：

mysql> select * from t1_delete;+----+----------------------------+| id | log_time                   |+----+----------------------------+|  1 | 2014-11-26 13:38:06.000000 || 12 | 2014-11-26 13:38:06.000000 || 13 | 2014-11-26 13:38:06.000000 || 14 | 2014-11-26 13:38:06.000000 |+----+----------------------------+4 rows in set (0.00 sec)