set a=1; -- 把1赋给变量a set b=a; -- 把 a的值赋给变量 b @XX 为用户变量 @@XXX 是系统变量
估计你还想问@@CHARACTER_SET_CLIENT; 这个系统变量是什么意思。建议查一下MYSQL的官方手册中的说明，几百个系统变量，否则你得一个一个问过来。character_set_client Variable Name character_set_client Variable Scope Both Dynamic Variable Yes Value Set Type string The character set for statements that arrive from the client. The session value of this variable is set using the character set requested by the client when the client connects to the server. (Many clients support a --default-character-set option to enable this character set to be specified explicitly. See also Section 9.1.4, “Connection Character Sets and Collations”.) The global value of the variable is used to set the session value in cases when the client-requested value is unknown or not available, or the server is configured to ignore client requests: The client is from a version of MySQL older than MySQL 4.1, and thus does not request a character set. The client requests a character set not known to the server. For example, a Japanese-enabled client requests sjis when connecting to a server not configured with sjis support. mysqld was started with the --skip-character-set-client-handshake option, which causes it to ignore client character set configuration. This reproduces MySQL 4.0 behavior and is useful should you wish to upgrade the server without upgrading all the clients.
set b=a; -- 把 a的值赋给变量 b
@XX 为用户变量
@@XXX 是系统变量
Variable Scope Both
Dynamic Variable Yes
Value Set Type string
The character set for statements that arrive from the client. The session value of this variable is set using the character set requested by the client when the client connects to the server. (Many clients support a --default-character-set option to enable this character set to be specified explicitly. See also Section 9.1.4, “Connection Character Sets and Collations”.) The global value of the variable is used to set the session value in cases when the client-requested value is unknown or not available, or the server is configured to ignore client requests: The client is from a version of MySQL older than MySQL 4.1, and thus does not request a character set. The client requests a character set not known to the server. For example, a Japanese-enabled client requests sjis when connecting to a server not configured with sjis support. mysqld was started with the --skip-character-set-client-handshake option, which causes it to ignore client character set configuration. This reproduces MySQL 4.0 behavior and is useful should you wish to upgrade the server without upgrading all the clients.