MySQL中show命令方法得到表列及整个库的详细信息(精品珍藏)
MySQL中show 句法得到表列及整个库的详细信息，方便查看数据库的详细信息。
show databases;
show tables from db_name;
show columns from table_name from db_name;
show index from talbe_name [from db_name];
show status;
show variables;
show [full] processlist;
show table status [from db_name];
show grants for user;
除了status,processlist和grants外，其它的都可以带有like wild选项，它可以使用SQL的'%'和'_'字符；
show databases like '%t';
将会列出所有数据库名字末尾为't'字符的数据库
当然了，在这些sql中，你也可以用db_name.table_name来代替 table_name from db_name这样写会更简便些!
如果一个用户没有一个表的任何权限，表将不在SHOW TABLES或mysqlshow db_name中的输出中显示
大家可能还记得describe table_name ，它实现的是与show columns from db_name.table_name一样的效果
show status将可以用mysqlshow --status 来得到同样的效果
SHOW FIELDS是SHOW COLUMNS一个同义词，SHOW KEYS是SHOW INDEX一个同义词。你也可以用mysqlshow db_name tbl_name或mysqlshow -k db_name tbl_name 列出一张表的列或索引。
SHOW INDEX以非常相似于ODBC的SQLStatistics调用的格式返回索引信息。下面的列被返回：
SHOW STATUS提供服务器的状态信息(象mysqladmin extended-status一样)。输出类似于下面的显示，尽管格式和数字可以有点不同：
+--------------------------+--------+<br>| Variable_name | Value |<br>+--------------------------+--------+<br>| Aborted_clients | 0 |<br>| Aborted_connects | 0 |<br>| Connections | 17 |<br>| Created_tmp_tables | 0 |<br>| Delayed_insert_threads | 0 |<br>| Delayed_writes | 0 |<br>| Delayed_errors | 0 |<br>| Flush_commands | 2 |<br>| Handler_delete | 2 |<br>| Handler_read_first | 0 |<br>| Handler_read_key | 1 |<br>| Handler_read_next | 0 |<br>| Handler_read_rnd | 35 |<br>| Handler_update | 0 |<br>| Handler_write | 2 |<br>| Key_blocks_used | 0 |<br>| Key_read_requests | 0 |<br>| Key_reads | 0 |<br>| Key_write_requests | 0 |<br>| Key_writes | 0 |<br>| Max_used_connections | 1 |<br>| Not_flushed_key_blocks | 0 |<br>| Not_flushed_delayed_rows | 0 |<br>| Open_tables | 1 |<br>| Open_files | 2 |<br>| Open_streams | 0 |<br>| Opened_tables | 11 |<br>| Questions | 14 |<br>| Slow_queries | 0 |<br>| Threads_connected | 1 |<br>| Threads_running | 1 |<br>| Uptime | 149111 |<br>+--------------------------+--------+
上面列出的状态变量有下列含义：
关于上面的一些注释：
- 如果
Opened_tables太大，那么你的table_cache变量可能太小。 - 如果
key_reads太大，那么你的key_cache可能太小。缓存命中率可以用key_reads/key_read_requests计算。 - 如果
Handler_read_rnd太大，那么你很可能有大量的查询需要MySQL扫描整个表或你有没正确使用键值的联结(join)。
SHOW VARIABLES显示出一些MySQL系统变量的值，你也能使用mysqladmin variables命令得到这个信息。如果缺省值不合适，你能在mysqld启动时使用命令行选项来设置这些变量的大多数。输出类似于下面的显示，尽管格式和数字可以有点不同：
+------------------------+--------------------------+<br>| Variable_name | Value |<br>+------------------------+--------------------------+<br>| back_log | 5 |<br>| connect_timeout | 5 |<br>| basedir | /my/monty/ |<br>| datadir | /my/monty/data/ |<br>| delayed_insert_limit | 100 |<br>| delayed_insert_timeout | 300 |<br>| delayed_queue_size | 1000 |<br>| join_buffer_size | 131072 |<br>| flush_time | 0 |<br>| interactive_timeout | 28800 |<br>| key_buffer_size | 1048540 |<br>| language | /my/monty/share/english/ |<br>| log | OFF |<br>| log_update | OFF |<br>| long_query_time | 10 |<br>| low_priority_updates | OFF |<br>| max_allowed_packet | 1048576 |<br>| max_connections | 100 |<br>| max_connect_errors | 10 |<br>| max_delayed_threads | 20 |<br>| max_heap_table_size | 16777216 |<br>| max_join_size | 4294967295 |<br>| max_sort_length | 1024 |<br>| max_tmp_tables | 32 |<br>| net_buffer_length | 16384 |<br>| port | 3306 |<br>| protocol-version | 10 |<br>| record_buffer | 131072 |<br>| skip_locking | ON |<br>| socket | /tmp/mysql.sock |<br>| sort_buffer | 2097116 |<br>| table_cache | 64 |<br>| thread_stack | 131072 |<br>| tmp_table_size | 1048576 |<br>| tmpdir | /machine/tmp/ |<br>| version | 3.23.0-alpha-debug |<br>| wait_timeout | 28800 |<br>+------------------------+--------------------------+<p><code>SHOW PROCESSLIST</code>显示哪个线程正在运行，你也能使用<code>mysqladmin processlist</code>命令得到这个信息。<br>如果你有<strong>process</strong>权限， 你能看见所有的线程，否则，你仅能看见你自己的线程。<br> 见7.20<code> KILL</code>句法。如果你不使用<code>FULL</code>选项，那么每个查询只有头100字符被显示出来。 </p><p><code>SHOW GRANTS FOR user</code>列出对一个用户必须发出以重复授权的授权命令。 </p><pre class="brush:php;toolbar:false">mysql> SHOW GRANTS FOR root@localhost;<br>+---------------------------------------------------------------------+<br>| Grants for root@localhost |<br>+---------------------------------------------------------------------+<br>| GRANT ALL PRIVILEGES ON *.* TO 'root''localhost' WITH GRANT OPTION |<br>+---------------------------------------------------------------------+
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