MYSQL 临时表用法总结

MYSQL 临时表用法总结

1.背景

老项目最近被吐槽性能不行，经排查发现mysql占用cpu过高，梳理流程发现一些经常被使用的字段需要多张表关联之后可获取，于是想到了临时表；

2.临时表用法总结

1. 将正常的CREATE TABLE语句改为CREATE TEMPORARY TABLE即可；
2. 临时表将在你连接MySQL期间存在。当你断开时，MySQL将自动删除表并释放所用的空间。当然你可以在仍然连接的时候删除表并释放空间。
3. 如果在你创建名为test_table_20200313临时表时名为test_table_20200313的表在数据库中已经存在，临时表将隐藏非临时表test_table_20200313；
4. 创建临时表时如果指定ENGINE=memory，系统会在内存中创建它；因为表存储在内存中，所以对它运行的查询可能比磁盘上的临时表快些；

2.1 磁盘临时表（和数据库其他表一样，都被存放在物理磁盘中）

mysql> CREATE TEMPORARY TABLE `test_table_20200313` (
    ->   `commandid` bigint(20) unsigned NOT NULL DEFAULT '0' COMMENT 'id',
    ->   `idcid` varchar(18) NOT NULL DEFAULT '' COMMENT '',
    ->   `add_time` varchar(19) NOT NULL DEFAULT '' COMMENT '',
    ->   `local` tinyint(1) NOT NULL DEFAULT '0'
    -> );
Query OK, 0 rows affected (0.00 sec)

mysql> INSERT INTO test_table_20200313 VALUES (369,'abc','123456789',0);
Query OK, 1 row affected (0.00 sec)

mysql> SELECT * FROM test_table_20200313;
+-----------+-------+-----------+-------+
| commandid | idcid | add_time  | local |
+-----------+-------+-----------+-------+
|       369 | abc   | 123456789 |     0 |
+-----------+-------+-----------+-------+
1 row in set (0.00 sec)

mysql> desc test_table_20200313;
+-----------+---------------------+------+-----+---------+-------+
| Field     | Type                | Null | Key | Default | Extra |
+-----------+---------------------+------+-----+---------+-------+
| commandid | bigint(20) unsigned | NO   |     | 0       |       |
| idcid     | varchar(18)         | NO   |     |         |       |
| add_time  | varchar(19)         | NO   |     |         |       |
| local     | tinyint(1)          | NO   |     | 0       |       |
+-----------+---------------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

mysql> show tables;
+---------------------+
| Tables_in_chang_dep |
+---------------------+
| emp                 |
| emp_bak             |
+---------------------+
2 rows in set (0.00 sec)

mysql> DROP TABLE test_table_20200313;
Query OK, 0 rows affected (0.00 sec)

2.2 内存临时表

mysql> CREATE TEMPORARY TABLE `test_table_20200313` (
    ->   `commandid` bigint(20) unsigned NOT NULL DEFAULT '0' COMMENT 'id',
    ->   `idcid` varchar(18) NOT NULL DEFAULT '' COMMENT '',
    ->   `add_time` varchar(19) NOT NULL DEFAULT '' COMMENT '',
    ->   `local` tinyint(1) NOT NULL DEFAULT '0'
    -> ) ENGINE=memory;
Query OK, 0 rows affected (0.00 sec)

mysql> INSERT INTO test_table_20200313 VALUES (369,'abc','123456789',0);
Query OK, 1 row affected (0.00 sec)

mysql> SELECT * FROM test_table_20200313;
+-----------+-------+-----------+-------+
| commandid | idcid | add_time  | local |
+-----------+-------+-----------+-------+
|       369 | abc   | 123456789 |     0 |
+-----------+-------+-----------+-------+
1 row in set (0.00 sec)

mysql> desc test_table_20200313;
+-----------+---------------------+------+-----+---------+-------+
| Field     | Type                | Null | Key | Default | Extra |
+-----------+---------------------+------+-----+---------+-------+
| commandid | bigint(20) unsigned | NO   |     | 0       |       |
| idcid     | varchar(18)         | NO   |     |         |       |
| add_time  | varchar(19)         | NO   |     |         |       |
| local     | tinyint(1)          | NO   |     | 0       |       |
+-----------+---------------------+------+-----+---------+-------+
4 rows in set (0.00 sec)

mysql> show tables;
+---------------------+
| Tables_in_chang_dep |
+---------------------+
| emp                 |
| emp_bak             |
+---------------------+
2 rows in set (0.00 sec)

mysql> DROP TABLE test_table_20200313;
Query OK, 0 rows affected (0.00 sec)

2.3 二者区别

1. 磁盘临时表建表时允许直接将查询结果导入临时表，且临时表中的字段类型和原表中的完全一致；内存临时表无法实现建表时直接将查询结果导入临时表；

mysql> CREATE TEMPORARY TABLE `test_table_20200313_1` (
    ->   `commandid` bigint(20) unsigned NOT NULL DEFAULT '0' COMMENT '指令id',
    ->   `idcid` varchar(18) NOT NULL DEFAULT '' COMMENT '许可证号',
    ->   `add_time` varchar(19) NOT NULL DEFAULT '' COMMENT '时间',
    ->   `local` tinyint(1) NOT NULL DEFAULT '0'
    -> );
Query OK, 0 rows affected (0.01 sec)

mysql> INSERT INTO test_table_20200313_1 VALUES (369,'abc','2222222222',0);
Query OK, 1 row affected (0.00 sec)

mysql> CREATE TEMPORARY TABLE `test_table_20200313_2` (
    ->   `commandid` bigint(20) unsigned NOT NULL DEFAULT '0' COMMENT '指令id',
    ->   `name` varchar(18) NOT NULL DEFAULT '' COMMENT '姓名'
    -> );
Query OK, 0 rows affected (0.01 sec)

mysql> INSERT INTO test_table_20200313_2 VALUES (369,'tom');
Query OK, 1 row affected (0.01 sec)

mysql> select a.commandid,a.idcid,b.name from test_table_20200313_1 a ,test_table_20200313_2 b where a.commandid=b.commandid and a.idcid='abc';
+-----------+-------+------+
| commandid | idcid | name |
+-----------+-------+------+
|       369 | abc   | tom  |
+-----------+-------+------+
1 row in set (0.00 sec)

mysql> CREATE TEMPORARY TABLE test_table_20200313
    -> (
    -> select a.commandid,a.idcid,b.name from test_table_20200313_1 a ,test_table_20200313_2 b where a.commandid=b.commandid and a.idcid='abc'
    -> );
Query OK, 1 row affected (0.02 sec)
Records: 1  Duplicates: 0  Warnings: 0

mysql> select * from test_table_20200313;
+-----------+-------+------+
| commandid | idcid | name |
+-----------+-------+------+
|       369 | abc   | tom  |
+-----------+-------+------+
1 row in set (0.00 sec)

mysql> desc test_table_20200313;
+-----------+---------------------+------+-----+---------+-------+
| Field     | Type                | Null | Key | Default | Extra |
+-----------+---------------------+------+-----+---------+-------+
| commandid | bigint(20) unsigned | NO   |     | 0       |       |
| idcid     | varchar(18)         | NO   |     |         |       |
| name      | varchar(18)         | NO   |     |         |       |
+-----------+---------------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

mysql> CREATE TEMPORARY TABLE test_table_20200313_mem
    -> (
    -> select a.commandid,a.idcid,b.name from test_table_20200313_1 a ,test_table_20200313_2 b where a.commandid=b.commandid and a.idcid='abc'
    -> ) ENGINE=memory;
ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'ENGINE=memory' at line 4
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