MySQL学习笔记--对变量(variable)用法方法的一点整理

icer_repls

我刚才也试验了一把。
版本
root@localhost test 02:28:55> SELECT version();
+---------------------+
| version()           |
+---------------------+
| 5.0.89-community-nt |
+---------------------+
1 row in set (0.00 sec)

session1：
root@localhost test 02:02:02> SELECT @@key_buffer_size;
+-------------------+
| @@key_buffer_size |
+-------------------+
|          13631488 |
+-------------------+
1 row in set (0.04 sec)
root@localhost test 02:19:27> SET GLOBAL VARIABLES key_buffer_size=100000;
ERROR 1193 (HY000): Unknown system variable 'VARIABLES'
root@localhost test 02:21:17> SET GLOBAL key_buffer_size=100000;
Query OK, 0 rows affected (0.11 sec)
root@localhost test 02:21:32> SELECT @@key_buffer_size;
+-------------------+
| @@key_buffer_size |
+-------------------+
|             98304 |
+-------------------+
1 row in set (0.00 sec)
root@localhost test 02:21:39> SHOW GLOBAL VARIABLES LIKE 'key_buffer_size';
+-----------------+-------+
| Variable_name   | Value |
+-----------------+-------+
| key_buffer_size | 98304 |
+-----------------+-------+
1 row in set (0.00 sec)
root@localhost test 02:22:24> SHOW SESSION VARIABLES LIKE 'key_buffer_size';
+-----------------+-------+
| Variable_name   | Value |
+-----------------+-------+
| key_buffer_size | 98304 |
+-----------------+-------+
1 row in set (0.00 sec)

session2：
root@localhost (none) 02:20:17> SELECT @@key_buffer_size;
+-------------------+
| @@key_buffer_size |
+-------------------+
|          13631488 |
+-------------------+
1 row in set (0.00 sec)
root@localhost (none) 02:20:50> SELECT @@key_buffer_size;
+-------------------+
| @@key_buffer_size |
+-------------------+
|             98304 |
+-------------------+
1 row in set (0.00 sec)
root@localhost (none) 02:22:58> SHOW GLOBAL VARIABLES LIKE 'key_buffer_size';
+-----------------+-------+
| Variable_name   | Value |
+-----------------+-------+
| key_buffer_size | 98304 |
+-----------------+-------+
1 row in set (0.00 sec)
root@localhost (none) 02:23:19> SHOW SESSION VARIABLES LIKE 'key_buffer_size';
+-----------------+-------+
| Variable_name   | Value |
+-----------------+-------+
| key_buffer_size | 98304 |
+-----------------+-------+
1 row in set (0.00 sec)

两个session同时打开的，确实不需要退出，然后再登陆。