文章目錄
前言
生活中有時會出現靈魂三問:我是誰?我在哪?我在做什麼?特別的喝醉酒的第二天,完全不記得昨天發生了什麼。而在數據庫操作中也會出現這種靈魂拷問,我用的是哪個用戶,爲什麼會沒有權限?我操作的是哪個數據庫,剛剛不會把線上正式服務器數據刪了吧?
上面描述的問題常常出現在切換數據庫處理問題的時候,通過一個客戶端連接到Mysql數據庫服務器,操作數據庫1,然後切換再操作數據庫2,這時如果中間有人打擾,很容易忘記剛剛操作的是哪個數據庫,或者中途處理個其他緊急的事情,回來連操作的用戶都忘了,這時就需要一些基礎信息的查詢命令,幫助你來恢復記憶。
數據庫基礎信息查詢
數據庫的基礎信息涉及到方方面面,這裏只列舉幾個常用的查詢命令,用來回答上面的靈魂拷問,其他命令還有很多,用到了再總結吧。
查詢當前操作的用戶
mysql> select user();
+----------------+
| user() |
+----------------+
| root@localhost |
+----------------+
1 row in set (0.07 sec)
查詢當前操作的數據庫
mysql> select database();
+------------+
| database() |
+------------+
| sqltest2 |
+------------+
1 row in set (0.09 sec)
查詢當前數據庫端口
mysql> show variables like 'port';
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| port | 3306 |
+---------------+-------+
1 row in set (0.07 sec)
查詢當前數據庫版本
mysql> select version();
+------------+
| version() |
+------------+
| 5.7.21-log |
+------------+
1 row in set (0.06 sec)
數據庫結構信息查詢
這裏的結構我指的是DDL
中定義的那些元素,比如表、存儲過程等,有一些常用的查詢命令,要是一段時間不使用還是會忘記,比如查詢一個數據庫中的存儲過程,每次查詢時都要上網搜一下,所以今天總結在一起方便查找。
查詢當前數據庫中的所有表
mysql> show tables;
+--------------------+
| Tables_in_sqltest2 |
+--------------------+
| a |
| b |
| c |
| d |
| m |
| p |
| tb_test |
| tb_with_index |
+--------------------+
14 rows in set (0.11 sec)
查詢創建表的sql語句
mysql> show create table a;
+-------+----------------------------------------+
| Table | Create Table |
+-------+----------------------------------------+
| a | CREATE TABLE `a` (
`id` int(11) DEFAULT NULL,
`num` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+----------------------------------------+
1 row in set (0.11 sec)
查詢指定表中的所有字段
mysql> desc a;
+-------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| id | int(11) | YES | | NULL | |
| num | int(11) | YES | | NULL | |
+-------+---------+------+-----+---------+-------+
2 rows in set (0.12 sec)
查詢當前數據庫中的所有存儲過程
這個命令我得吐槽一下,爲什麼不能像查詢當前數據庫的中所有表一樣,搞個show procedures;
命令,非得通過where子句指定數據庫呢,具體的原因還不知道,等我弄明白了再回來補充。
mysql> show procedure status where db='sqltest2';
+----------+-----------------------+-----------+----------------+---------------------+---------------------+---------------+---------+----------------------+----------------------+--------------------+
| Db | Name | Type | Definer | Modified | Created | Security_type | Comment | character_set_client | collation_connection | Database Collation |
+----------+-----------------------+-----------+----------------+---------------------+---------------------+---------------+---------+----------------------+----------------------+--------------------+
| sqltest2 | fill_slow_query_test | PROCEDURE | root@localhost | 2019-03-25 11:14:01 | 2019-03-25 11:14:01 | DEFINER | | utf8mb4 | utf8mb4_general_ci | utf8_general_ci |
| sqltest2 | fill_tb_without_index | PROCEDURE | root@localhost | 2019-03-18 09:53:32 | 2019-03-18 09:53:32 | DEFINER | | utf8mb4 | utf8mb4_general_ci | utf8_general_ci |
| sqltest2 | fill_tb_with_index | PROCEDURE | root@localhost | 2019-03-18 09:53:33 | 2019-03-18 09:53:33 | DEFINER | | utf8mb4 | utf8mb4_general_ci | utf8_general_ci |
+----------+-----------------------+-----------+----------------+---------------------+---------------------+---------------+---------+----------------------+----------------------+--------------------+
3 rows in set (0.17 sec)
查詢創建存儲過程的sql語句
mysql> show create procedure fill_tb_with_index;
+--------------------+----------------------------------------------------------------+-------------------+----------------------+----------------------+--------------------+
| Procedure | sql_mode | Create Procedure | character_set_client | collation_connection | Database Collation |
+--------------------+----------------------------------------------------------------+-------------------+----------------------+----------------------+--------------------+
| fill_tb_with_index | STRICT_TRANS_TABLES,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION |
CREATE DEFINER=`root`@`localhost` PROCEDURE `fill_tb_with_index`()
BEGIN
DECLARE i int default 1;
WHILE i <= 100000 do
insert into tb_with_index values(i, i, i);
set i = i + 1;
END WHILE;
END | utf8mb4 | utf8mb4_general_ci | utf8_general_ci |
+--------------------+----------------------------------------------------------------+-------------------+----------------------+----------------------+--------------------+
1 row in set (0.09 sec)
查詢指定表上的索引
mysql> show index from tb_with_index;
+---------------+------------+-------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| Table | Non_unique | Key_name | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment | Index_comment |
+---------------+------------+-------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
| tb_with_index | 1 | id_index | 1 | id | A | 100035 | NULL | NULL | YES | BTREE | | |
| tb_with_index | 1 | num_index | 1 | num | A | 98715 | NULL | NULL | YES | BTREE | | |
| tb_with_index | 1 | money_index | 1 | money | A | 100035 | NULL | NULL | YES | BTREE | | |
+---------------+------------+-------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+---------------+
3 rows in set (0.03 sec)
查詢當前用戶連接的權限
mysql> show grants;
+---------------------------------------------------------------------+
| Grants for root@localhost |
+---------------------------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'root'@'localhost' WITH GRANT OPTION |
| GRANT PROXY ON ''@'' TO 'root'@'localhost' WITH GRANT OPTION |
+---------------------------------------------------------------------+
查詢指定用戶連接的權限
mysql> show grants for 'guest';
+---------------------------------------------------------------------------------------------------------------+
| Grants for guest@% |
+---------------------------------------------------------------------------------------------------------------+
| GRANT ALL PRIVILEGES ON *.* TO 'guest'@'%' IDENTIFIED BY PASSWORD '*6C8DE74065898C44C21EF74D67A834C5256BFA1C' |
+---------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
總結
- 以上總結的查詢語句都是我經常用到,相比Mysql所有查詢語句來說簡直是冰山一角,總結到一起主要是方便日後查找,同時也希望給他人帶來幫助
- 查看這些語句會發現,有些是
select
開頭,有些是show
開頭,實際上很多show
開頭的都是對information_schema
數據庫數據的封裝 information_schema
數據庫是Mysql系統自帶的數據庫,記錄了整個數據庫實例上所有數據結構信息,更像是記錄數據庫的數據庫,包含表結構、字符集,權限等太多的信息,有機會後續找時間聊聊這個數據庫,在此就不展開了- 正因爲很多
show
開頭的都是對information_schema
數據庫數據的封裝,所以這些查詢語句基本都可以通過在information_schema
數據庫查詢得到,比如show procedure status where db='sqltest2';
就可以改寫成select routine_name from information_schema.routines where routine_schema='sqltest2';
- 此時此刻,我正在距離天安門500多米的現場等待閱兵儀式的開始,一邊學習一邊爲祖國慶生的感覺真好!
(注:500多米多了5公里,現場是臥室牀前的電視機旁,這麼近的距離不知道一會能不能看見接受檢閱的飛機o(* ̄︶ ̄*)o)