1.mysqladminで調べる
2.mysqlコマンドで調べる
3.mysql接続時に表示
4.接続後statusコマンドで調べる
5.version関数で調べる
ざっと思いつくのでこの5種類。
その他にもあるだろうけど。

1.mysqladminで調べる
パスワード未設定ならオプションは不要

> mysqladmin -u user -p version
Enter password:
mysqladmin  Ver 8.41 Distrib 5.0.32, for pc-linux-gnu on i486
Copyright (C) 2000 MySQL AB & MySQL Finland AB & TCX DataKonsult AB
This software comes with ABSOLUTELY NO WARRANTY. This is free software,
and you are welcome to modify and redistribute it under the GPL license

Server version          5.0.32-Debian_7etch1-log
Protocol version        10
Connection              Localhost via UNIX socket
UNIX socket             /var/run/mysqld/mysqld.sock
Uptime:                 46 min 48 sec

Threads: 1  Questions: 135 Slow queries: 0 Opens: 136 Flush tables: 1 Open tables: 18 Queries per second avg: 0.048

2.mysqlコマンドで調べる

>mysql --version
mysql  Ver 14.12 Distrib 5.0.32, for pc-linux-gnu (i486) using readline 5.2

3.mysql接続時に表示

>mysql -u user -p test
Enter password:
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 11
Server version: 5.0.32-Debian_7etch1-log Debian etch distribution

Type 'help;' or '\h' for help. Type '\c' to clear the buffer.

mysql>

4.接続後statusコマンドで調べる

> status
--------------
mysql  Ver 14.12 Distrib 5.0.32, for pc-linux-gnu (i486) using readline 5.2

Connection id:          11
Current database:       test
Current user:           user@localhost
SSL:                    Not in use
Current pager:          stdout
Using outfile:          ''
Using delimiter:        ;
Server version:         5.0.32-Debian_7etch1-log Debian etch distribution
Protocol version:       10
Connection:             Localhost via UNIX socket
Server characterset:    utf8
Db     characterset:    utf8
Client characterset:    utf8
Conn.  characterset:    utf8
UNIX socket:            /var/run/mysqld/mysqld.sock
Uptime:                 6 min 38 sec

Threads:2 Questions: 162  Slow queries: 0  Opens: 136  Flush tables: 1 Open tables: 18 Queries per second avg: 0.407
--------------

5.version関数で調べる

> SELECT version();
+--------------------------+
| version()                |
+--------------------------+
| 5.0.32-Debian_7etch1-log |
+--------------------------+
1 row in set (0.00 sec)