檢視支援的引擎

mysql> show engines;
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| Engine             | Support | Comment                                                        | Transactions | XA   | Savepoints |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
| InnoDB             | DEFAULT | Supports transactions, row-level locking, and foreign keys     | YES          | YES  | YES        |
| MRG_MYISAM         | YES     | Collection of identical MyISAM tables                          | NO           | NO   | NO         |
| MEMORY             | YES     | Hash based, stored in memory, useful for temporary tables      | NO           | NO   | NO         |
| BLACKHOLE          | YES     | /dev/null storage engine (anything you write to it disappears) | NO           | NO   | NO         |
| MyISAM             | YES     | MyISAM storage engine                                          | NO           | NO   | NO         |
| CSV                | YES     | CSV storage engine                                             | NO           | NO   | NO         |
| ARCHIVE            | YES     | Archive storage engine                                         | NO           | NO   | NO         |
| PERFORMANCE_SCHEMA | YES     | Performance Schema                                             | NO           | NO   | NO         |
| FEDERATED          | NO      | Federated MySQL storage engine                                 | NULL         | NULL | NULL       |
+--------------------+---------+----------------------------------------------------------------+--------------+------+------------+
9 rows in set (0.01 sec)

 

Memory表被儲存在記憶體中。且預設使用雜湊索引。這使得它們很快，而且對建立暫時表很實用。但是。當server關閉之時，全部儲存在Memory表裡的資料被丟失。

由於表的定義被存在磁碟上的.frm檔案裡，所以表自身繼續存在。在server重新啟動動時它們是空的。

要明白指出你想要一個Memory表。可使用ENGINE選項來指定：

CREATE TABLE t (i INT) ENGINE = MEMORY;

CREATE TABLE test ENGINE=MEMORY;
SELECT ip,SUM(downloads) AS down FROM log_table GROUP BY ip;
SELECT COUNT(ip),AVG(down) FROM test;
DROP TABLE test;