【SQL篇章--DATABASE/EVENTS】

【SQL篇章】【SQL语句梳理 :--基于MySQL5.6】【已梳理：DATABASE/EVENTS】【会坚持完善】

 

目录:

1. Data Definition Statements:

　　1.1 create database, alter database, show databases

　　1.2 create event, alter event, show events

 

 

1. Data Definition Statements:

1.1

CREATE DATABASE

格式：

CREATE {DATABASE | SCHEMA} [IF NOT EXISTS] db_name [create_specification] create_specification :
　　[DEFAULT] CHARACTER SET [=] charset_name
　　[DEFAULT] COLLATE [=] collation_name

　　

事例 :

CREATE DATABASE db2;
CREATE DATABASE `db2` /*!40100 DEFAULT CHARACTER SET latin1 */

 

查看：

SHOW DATABASES;

ALTER DATABASE

格式：

ALTER {DATABASE | SCHEMA} [db_name]
　　alter_specification ...
ALTER {DATABASE | SCHEMA} db_name
　　UPGRADE DATA DIRECTORY NAME

alter_specification:
　　[DEFAULT] CHARACTER SET [=] charset_name  | [DEFAULT] COLLATE [=] collation_name

　　

 

事例操作：

<1> -->db1:utf8

ALTER DATABASE db1 CHARACTER SET = utf8;

 

查看：

mysql> SELECT * FROM information_schema.`SCHEMATA` WHERE schema_name='db1';
+--------------+-------------+----------------------------+------------------------+----------+
| CATALOG_NAME | SCHEMA_NAME | DEFAULT_CHARACTER_SET_NAME | DEFAULT_COLLATION_NAME | SQL_PATH |
+--------------+-------------+----------------------------+------------------------+----------+
| def          | db1         | utf8                       | utf8_general_ci        | NULL     |
+--------------+-------------+----------------------------+------------------------+----------+
1 row in set (0.04 sec)

　　

<2> -->db1:utf8-->latin1

ALTER DATABASE db1 CHARACTER SET = latin1;

　　

查看：

mysql> SELECT * FROM information_schema.`SCHEMATA` WHERE schema_name='db1';
+--------------+-------------+----------------------------+------------------------+----------+
| CATALOG_NAME | SCHEMA_NAME | DEFAULT_CHARACTER_SET_NAME | DEFAULT_COLLATION_NAME | SQL_PATH |
+--------------+-------------+----------------------------+------------------------+----------+
| def          | db1         | latin1                     | latin1_swedish_ci      | NULL     |
+--------------+-------------+----------------------------+------------------------+----------+
1 row in set (0.00 sec)

　　

<3> --创建表t5:  <db1:latin1>

CREATE TABLE t5(id int);

　　查看所建立表的字符集

mysql> SHOW CREATE TABLE db1.t5;
+-------+----------------------------------------------------------------------------------------+
| Table | Create Table                                                                           |
+-------+----------------------------------------------------------------------------------------+
| t5    | CREATE TABLE `t5` (
  `id` int(11) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1 |
+-------+----------------------------------------------------------------------------------------+
1 row in set (0.00 sec)

　　测试发现：

　　1.db的character改变后，collation随之改变。
　　2.db中旧表character不会改变。新建表character默认为与当前db相同。

　　

 

SHOW DATABASES;

格式：

SHOW {DATABASES | SCHEMAS} [LIKE 'pattern' | WHERE expr]

 

DROP DATABASE;

格式：

DROP {DATABASE | SCHEMA} [IF EXISTS] db_name

 

　　1.IF EXISTS : DB不存在，不会报错

　　2.DB drop掉，对应的物理目录也会删除。但是DB对应目录下有其它文件，无法执行drop DB的操作，报错

mysql> drop database wb;
ERROR 1010 (HY000): Error dropping database (can't rmdir './wb/', errno: 17)

　　

删除非数据库目录或文件：

mysql> drop database wb;
Query OK, 0 rows affected (0.00 sec)

　　

1.2

CREATE EVENT

格式：

CREATE
[DEFINER = { user | CURRENT_USER }]
EVENT
[IF NOT EXISTS]
event_name
ON SCHEDULE schedule
[ON COMPLETION [NOT] PRESERVE]
[ENABLE | DISABLE | DISABLE ON SLAVE]
[COMMENT 'comment']
DO event_body;

schedule:
AT timestamp [+ INTERVAL interval] ...
| EVERY interval
[STARTS timestamp [+ INTERVAL interval] ...]
[ENDS timestamp [+ INTERVAL interval] ...]

interval:
quantity {YEAR | QUARTER | MONTH | DAY | HOUR | MINUTE |
WEEK | SECOND | YEAR_MONTH | DAY_HOUR | DAY_MINUTE |
DAY_SECOND | HOUR_MINUTE | HOUR_SECOND | MINUTE_SECOND}

　　

注意事项：

• 创建event需要：event，super权限，建好之后，必须是enable状态。
• ON SCHEDULE ： 决定什么时间或者多长时间，时间执行一次
• DO :包含被event执行的SQL语句

默认 EVENT 支持是没有启动的，可以通过下面的命令来查看状态：

Select @@event_scheduler;

　　

如果返回 OFF ，则需要执行下面的命令启动：

SET GLOBAL event_scheduler = ON;

　　

好了，上面虽然启动了 EVENT ，但是每次重启 mysql 之后 EVENT 并没有自动启动，那么如何让它自动启动呢？

方法一：找到当前使用的 .cnf 文件

[mysqld]
event_scheduler=1

　　

方法二：启动 mysql 的时候增加 --event_scheduler=1

mysql start --event_scheduler=1

　　

事例：

1.只执行一次

CREATE
DEFINER = CURRENT_USER
EVENT IF NOT EXISTS myevent
ON SCHEDULE AT CURRENT_TIMESTAMP + INTERVAL 1 SECOND
DO
INSERT INTO db1.t1 VALUES(1);

　　

2.每隔一秒执行一次

CREATE
DEFINER = CURRENT_USER
EVENT IF NOT EXISTS myevent
ON SCHEDULE EVERY 1 SECOND
DO
INSERT INTO db1.t1 VALUES(1);

　　

3.event的执行时间是过去时，在创建时，就drop掉了，当前创建的event是没有显示的。

mysql> SELECT NOW();
+---------------------+
| NOW()               |
+---------------------+
| 2016-11-16 10:01:39 |
+---------------------+
1 row in set (0.00 sec)

mysql> CREATE EVENT event_1
    -> ON SCHEDULE AT '2006-02-10 23:59:00'
    -> DO INSERT INTO test.totals VALUES (NOW());
Query OK, 0 rows affected, 1 warning (0.00 sec)

mysql> SHOW WARNINGS\G
*************************** 1. row ***************************
  Level: Note
   Code: 1588
Message: Event execution time is in the past and ON COMPLETION NOT PRESERVE is set. The event was dropped immediately after creation.
1 row in set (0.00 sec)

 

ON SCHEDULE 解析：

1.

'two minutes and three seconds from now'

AT CURRENT_TIMESTAMP + INTERVAL '2:3' MINUTE_SECOND

'three weeks and two days from now'

AT CURRENT_TIMESTAMP + INTERVAL 3 WEEK + INTERVAL 2 DAY

 

2.

间隔值频率相同，可以用EVERY，不与'+INTERVAL'同时存在

ON SCHEDULE EVERY 6 WEEK

STARTS: 后面紧接timestamp,指示从什么时间开始执行repeating，可以用：+ INTERVAL interval 指示：从现在开始经多长时间后开始执行repeating.

eg1:'every three months, beginning one week from now':从现在开始1周之后，开始执行，每隔3月的重复操作。

EVERY 3 MONTH STARTS CURRENT_TIMESTAMP + INTERVAL 1 WEEK means

eg2:'every two weeks, beginning six hours and fifteen minutes from now'

EVERY 2 WEEK STARTS CURRENT_TIMESTAMP + INTERVAL '6:15' HOUR_MINUTE.

 

ENDS : 同starts相反，指示从什么时间停止执行repeating。用法同starts

eg: 'every twelve hours, beginning thirty minutes from now, and ending four weeks from now'

EVERY 12 HOUR STARTS CURRENT_TIMESTAMP + INTERVAL 30 MINUTE ENDS CURRENT_TIMESTAMP + INTERVAL 4 WEEK

备注：STARTS,ENDS,可以同时使用，也可用其一，也可以使用复杂的时间单元

 

[ON COMPLETION [NOT] PRESERVE] 解析：

1. 正常来说，一旦event过期，会立即drop掉。
2. 可以通过设置：ON COMPLETION PRESERVE,来禁止drop操作。此时，event的状态从：ENABLE---->DISABLE。EVENT停止执行，保留存在。
3. 可以通过设置：ON COMLETION NOT PRESERVE,不禁止drop操作，此时，event执行完毕，会立即drop掉。此时看不到event了。
4. 在不指定时，默认：COMPLETION NOT PRESERVE ENABLE .也就是说，event过期后会自动drop。

测试事例：

eg:

CREATE DEFINER=CURRENT_USER EVENT IF NOT EXISTS myevent
ON SCHEDULE EVERY 1 SECOND STARTS CURRENT_TIMESTAMP + INTERVAL 1 MINUTE ENDS CURRENT_TIMESTAMP + INTERVAL 3 MINUTE
DO
INSERT INTO db1.`t1`(id) VALUES(5);

 

创建完成，再次查看event：

DELIMITER $$
ALTER DEFINER=`admin`@`%` EVENT `myevent` 
ON SCHEDULE EVERY 1 SECOND STARTS '2016-11-30 16:42:02' ENDS '2016-11-30 16:44:02' 
ON COMPLETION NOT PRESERVE ENABLE 
DO INSERT INTO db1.`t1`(id) VALUES(5)$$
DELIMITER ;

　　

[ENABLE | DISABLE | DISABLE ON SLAVE]解析；

通过设置：ENABLE：启动event；DISABLE：停止event。在ALTER EVENT时，很常用。

DISABLE ON SLAVE : 设置主从复制时，标示从库的event的状态。event会在master上创建，并复制到从库，但是不会在从库上执行。

 

测试事例：

CREATE DEFINER=CURRENT_USER EVENT IF NOT EXISTS myevent
ON SCHEDULE EVERY 1 SECOND STARTS CURRENT_TIMESTAMP + INTERVAL 1 MINUTE ENDS CURRENT_TIMESTAMP + INTERVAL 3 MINUTE
ON COMPLETION PRESERVE ENABLE
DO
INSERT INTO db1.t1(id) VALUES(1);

观察master 和 slave上event的结构：　　

MASTER:

DELIMITER $$
ALTER DEFINER=`admin`@`%` EVENT `myevent` 
ON SCHEDULE EVERY 1 SECOND STARTS '2016-11-16 01:35:40' ENDS '2016-11-16 01:37:40' 
ON COMPLETION PRESERVE ENABLE DO INSERT INTO db1.t1(id) VALUES(1)$$
DELIMITER ;

　　

SLAVE:

DELIMITER $$
ALTER DEFINER=`admin`@`%` EVENT `myevent` 
ON SCHEDULE EVERY 1 SECOND STARTS '2016-11-16 01:35:40' ENDS '2016-11-16 01:37:40' 
ON COMPLETION PRESERVE DISABLE ON SLAVE DO INSERT INTO db1.t1(id) VALUES(1)$$
DELIMITER ;

 

通过系统表EVENTS查看状态

MASTER:

mysql> SELECT EVENT_SCHEMA,EVENT_NAME,STATUS FROM `information_schema`.`EVENTS` WHERE EVENT_SCHEMA='db1';
+--------------+------------+----------+
| EVENT_SCHEMA | EVENT_NAME | STATUS   |
+--------------+------------+----------+
| db1          | myevent    | DISABLED |
+--------------+------------+----------+
1 row in set (0.00 sec)　

SLAVE:

mysql> SELECT EVENT_NAME,STATUS FROM `information_schema`.`EVENTS`;
+------------+--------------------+
| EVENT_NAME | STATUS             |
+------------+--------------------+
| myevent    | SLAVESIDE_DISABLED |
+------------+--------------------+

[COMMENT 'comment']解析：

描述EVENT,最多64字符，用引号引起来。

 

DO 解析：

指定EVENT所执行的动作，可以是任何SQL。

 

SQL_MODE 解析:

mysql> SELECT SQL_MODE FROM information_schema.`EVENTS`;
+--------------------------------------------+
| SQL_MODE |
+--------------------------------------------+
| STRICT_TRANS_TABLES,NO_ENGINE_SUBSTITUTION |
+--------------------------------------------+

　　

对EVENT执行create ，alter操作时，MYSQL存储的SQL_MODE系统变量总是被强制设置。

regardless of the current server SQL mode when the event begins executing.

 

DO 中使用复合语句

select,show 在event中是没有效果的。但是可以使用：select. . . insert, insert into . . . select

复合语句在event中，可以使用EBGIN,END关键字：

1.

DELIMITER $$
CREATE EVENT e_count1
ON SCHEDULE
EVERY 4 SECOND
COMMENT 'Saves total number of tb1'
DO
BEGIN
INSERT INTO t2(TIME,total) SELECT CURRENT_TIMESTAMP,COUNT(*) FROM t1;
DELETE FROM t1;
END $$
DELIMITER ;

　　

 

2.下面的event中应用了：本地变量、错误处理、流控制结构

DELIMITER $$

CREATE EVENT e
ON SCHEDULE
EVERY 5 SECOND
DO
BEGIN
DECLARE v INTEGER;
DECLARE CONTINUE HANDLER FOR SQLEXCEPTION BEGIN END;
SET v = 0;

WHILE v < 5 DO
INSERT INTO t3 VALUES(0);
UPDATE t3 SET s1 = s1 + 1;
SET v = v + 1;
END WHILE;
END $$
DELIMITER ;

　　

EVENT中调用存储过程

CREATE EVENT e_call_myproc
ON SCHEDULE
AT CURRENT_TIMESTAMP + INTERVAL 1 DAY
DO CALL myproc(5, 27);

 

ALTER EVENT;

格式：

ALTER
[DEFINER = { user | CURRENT_USER }]
EVENT event_name
[ON SCHEDULE schedule]
[ON COMPLETION [NOT] PRESERVE]
[RENAME TO new_event_name]
[ENABLE | DISABLE | DISABLE ON SLAVE]
[COMMENT 'comment']
[DO event_body]

事例操作：

主干语句：ALTER EVENT event_name；

1.前提EVENT必须存在

mysql> alter event event1 on schedule every '2:3' DAY_HOUR ;
ERROR 1539 (HY000): Unknown event 'event1'

　　

2.

ALTER EVENT myevent
ON SCHEDULE
EVERY 2 SECOND STARTS CURRENT_TIMESTAMP + INTERVAL 1 MINUTE ENABLE
DO
INSERT INTO t2(TIME,total) VALUES(CURRENT_TIMESTAMP,5);

　　

3.停止event

ALTER EVENT myevent DISABLE;

　　

4.EVENT改名

ALTER EVENT olddb.myevent RENAME TO newdb.myevent;

　　

SHOW EVENTS:

格式：

SHOW EVENTS [{FROM | IN} schema_name] [LIKE 'pattern' | WHERE expr]

　　

事例：

<1>

show events; 列出当前DB中所有events。

mysql> select current_user(),schema();
+-----------------+----------+
| current_user() | schema() |
+-----------------+----------+
| admin@localhost | db1 |
+-----------------+----------+
1 row in set (0.00 sec)

　　

mysql> show events\G
*************************** 1. row ***************************
                  Db: db1
                Name: myevent
             Definer: admin@%
           Time zone: SYSTEM
                Type: RECURRING
          Execute at: NULL
      Interval value: 2
      Interval field: SECOND
              Starts: 2016-11-16 08:37:26
                Ends: 2016-11-16 01:44:11
              Status: DISABLED
          Originator: 5
character_set_client: utf8
collation_connection: utf8_general_ci
  Database Collation: utf8_general_ci
1 row in set (0.07 sec)

 

<2>

列出指定DB下的events

SHOW EVENTS FROM wb;
SHOW EVENTS FROM wb like '%wb';

　　

<3> show events输出关键词解析：

 

Type: EVENT的重复执行类型 ONE TIME (transient) or RECURRING (repeating).

Execute：  执行一次的event显示：AT

　　　　　　重复执行的event显示NULL

Interval value: 2 一次执行完毕到下次执行时的间隔。

Interval field: SECOND 执行间隔时间单位

Status: event的状态

Originator MySQL server 的 ID

 

<4>

SHOW CREATE EVENT event_name;

　　

mysql> show create event myevent\G
*************************** 1. row ***************************
Event: myevent
sql_mode: STRICT_TRANS_TABLES,NO_ENGINE_SUBSTITUTION
time_zone: SYSTEM
Create Event: CREATE DEFINER=`admin`@`%` EVENT `myevent` 
ON SCHEDULE EVERY 2 SECOND STARTS '2016-11-16 08:37:26' ENDS '2016-11-16 01:44:11' 
ON COMPLETION PRESERVE DISABLE 
DO insert into t2(Time,total) values(current_timestamp,5)
character_set_client: utf8
collation_connection: utf8_general_ci
Database Collation: utf8_general_ci
1 row in set (0.00 sec)

　　

DROP EVENTS

格式：

DROP EVENT [IF EXISTS] event_name

　　

1.删除不存在的EVENT,报错

mysql> DROP EVENT E;
ERROR 1539 (HY000): Unknown event 'E'

　　

2.EVENT不存在，消除报错

mysql> DROP EVENT IF EXISTS E;
Query OK, 0 rows affected, 1 warning (0.00 sec)

　　

3.EVENT存在，正常删除

mysql> DROP EVENT e_1;
Query OK, 0 rows affected (0.00 sec)