MySql常用操作语句(2:数据库、表管理以及数据操作)

时间:2022-02-04 20:41:34

  本文主要内容转自一博文

  另外可供参考资源:

  SQL语句教程

  SQL语法

  1、数据库(database)管理

   1.1 create 创建数据库

mysql> create database firstDB;

   1.2 show 查看所有数据库

mysql> show databases;

+--------------------+
| Database |
+--------------------+
| information_schema |
| firstDB |
| mysql |
| performance_schema |
+--------------------+
4 rows in set (0.00 sec)

   1.3 alter 修改数据库

  alter 命令修改数据库编码:

  默认创建的数据库默认不支持中文字符,如果我们需要它支持中文字符,则将它的编码设置为utf8格式:

mysql> ALTER DATABASE testDB CHARACTER SET UTF8;
Query OK, 1 row affected (0.00 sec)

   1.4 use 使用数据库

mysql> use firstDB;
Database changed

   1.5 查看当前使用的数据库

mysql> select database();
+------------+
| database() |
+------------+
| firstdb |
+------------+
1 row in set (0.00 sec)

   1.6 drop 删除数据库

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

  2、数据表(table)管理

  我们首先创建一个数据库,提供我们往后的使用:

mysql> create database testDB;
Query OK, 1 row affected (0.00 sec)

  创建后记得用use命令进入(使用)数据库,不然后面的操作都会不成功的。

  2.1 create 创建表

mysql> create table PEOPLE (
-> ID int AUTO_INCREMENT PRIMARY KEY,
-> NAME varchar(20) not null,
-> AGE int not null,
-> BIRTHDAY datetime);
Query OK, 0 rows affected (0.01 sec)

   2.2 show 显示表

  显示当前数据库所有的数据表

mysql> show tables;
+------------------+
| Tables_in_testdb |
+------------------+
| PEOPLE |
+------------------+
1 row in set (0.00 sec)

   2.3 desc 查看表结构

mysql> desc PEOPLE
-> ;
+----------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+----------------+
| ID | int(11) | NO | PRI | NULL | auto_increment |
| NAME | varchar(20) | NO | | NULL | |
| AGE | int(11) | NO | | NULL | |
| BIRTHDAY | datetime | YES | | NULL | |
+----------+-------------+------+-----+---------+----------------+
4 rows in set (0.01 sec)

   2.4 alter 修改表结构(增、删、改)

  默认创建的表不支持中文字符,所以需将表编码设置为utf8:

mysql> ALTER TABLE KEYCHAIN CONVERT TO CHARACTER SET UTF8;
Query OK, 1 row affected (0.02 sec)
Records: 1 Duplicates: 0 Warnings: 0

   2.4.1 insert 在表中添加列(字段)

mysql> alter table PEOPLE add star BOOL;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0

  提示:在MySQL里,布尔类型会自动转换为tinyint(1)类型。

  我们不妨使用desc去查看一下PEOPLE表结构:

mysql> desc PEOPLE;
+----------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+----------------+
| ID | int(11) | NO | PRI | NULL | auto_increment |
| NAME | varchar(20) | NO | | NULL | |
| AGE | int(11) | NO | | NULL | |
| BIRTHDAY | datetime | YES | | NULL | |
| star | tinyint(1) | YES | | NULL | |
+----------+-------------+------+-----+---------+----------------+
5 rows in set (0.00 sec)

   2.4.2 alter 修改表(列)字段

mysql> alter table PEOPLE MODIFY star int;
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0

  也可以指定 int(n) 的长度,比如 int(2)。

  我们再次使用desc查看PEOPLE表结构:

mysql> desc PEOPLE;
+----------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+----------------+
| ID | int(11) | NO | PRI | NULL | auto_increment |
| NAME | varchar(20) | NO | | NULL | |
| AGE | int(11) | NO | | NULL | |
| BIRTHDAY | datetime | YES | | NULL | |
| star | int(11) | YES | | NULL | |
+----------+-------------+------+-----+---------+----------------+
5 rows in set (0.00 sec)

   2.4.3 delete 删除表(列)字段

mysql> alter table PEOPLE DROP column star;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0

  删除后,再次查看PEOPLE表结构:

mysql> desc PEOPLE;
+----------+-------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+----------------+
| ID | int(11) | NO | PRI | NULL | auto_increment |
| NAME | varchar(20) | NO | | NULL | |
| AGE | int(11) | NO | | NULL | |
| BIRTHDAY | datetime | YES | | NULL | |
+----------+-------------+------+-----+---------+----------------+
4 rows in set (0.00 sec)

  删除字段成功,现在我们已经不能看到star的字段了。

   2.4.4 rename 重命名表名

mysql> RENAME TABLE PEOPLE TO NEW_PEOPLE;
Query OK, 0 rows affected (0.00 sec)

   2.4.5 null or not null

  修改表字段允许为空或不允许为空:

mysql> ALTER TABLE PEOPLE MODIFY AGE INT(3) NULL;
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0

  把 PEOPLE 表的 AGE 字段设置成“允许为空”,即插入记录时这个字段可以不录入。否则相反。

  它的格式为:ALTER TABLE <TALBE_NAME> MODIFY <CLOUMN>  <NULL 'OR'  NOT NULL>

   2.5 create 利用已有数据创建新表

mysql> create table newTable select * from PEOPLE;
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0

  我们查看一下目前数据库存在的表:

mysql> show tables;
+------------------+
| Tables_in_testdb |
+------------------+
| PEOPLE |
| newTable |
+------------------+
2 rows in set (0.00 sec)

  3、数据的操作及管理

  数据表的基本操作,包含增、删、改、查数据。

  以下命令均在PEOPLE表上操作。

   3.1 增加数据(增)

  PEOPLE表目前是没有数据的,它是空的数据表,我们现在先添加一些数据。

  insert into 命令添加数据:

mysql> insert into PEOPLE VALUES (null, 'Anny', 22, '1992-05-22');
Query OK, 1 row affected (0.00 sec)

  使用select命令查看表(会在后面介绍),现在我们查看PEOPLE数据表的数据:

mysql> select * from PEOPLE;
+----+------+-----+---------------------+
| ID | NAME | AGE | BIRTHDAY |
+----+------+-----+---------------------+
| 1 | Anny | 22 | 1992-05-22 00:00:00 |
+----+------+-----+---------------------+
1 row in set (0.00 sec)

  数据表现在有一条数据。

我们多添加几条数据,如:

mysql> select * from PEOPLE;
+----+--------+-----+---------------------+
| ID | NAME | AGE | BIRTHDAY |
+----+--------+-----+---------------------+
| 1 | Anny | 22 | 1992-05-22 00:00:00 |
| 2 | Garvey | 23 | 1991-05-22 00:00:00 |
| 3 | Lisa | 25 | 1989-05-22 00:00:00 |
| 4 | Nick | 24 | 1990-05-22 00:00:00 |
| 5 | Rick | 24 | 1991-05-22 00:00:00 |
+----+--------+-----+---------------------+
5 rows in set (0.00 sec)

   3.2 删除数据(删)

  delete 命令删除数据:

mysql> delete from PEOPLE where name = 'Lisa';
Query OK, 1 row affected (0.01 sec)

  再次查询PEOPLE表:

mysql> select * from PEOPLE;
+----+--------+-----+---------------------+
| ID | NAME | AGE | BIRTHDAY |
+----+--------+-----+---------------------+
| 1 | Anny | 22 | 1992-05-22 00:00:00 |
| 2 | Garvey | 23 | 1991-05-22 00:00:00 |
| 4 | Nick | 24 | 1990-05-22 00:00:00 |
| 5 | Rick | 24 | 1991-05-22 00:00:00 |
+----+--------+-----+---------------------+
4 rows in set (0.00 sec)

  已经看不到名为“Lisa”的数据了。

  注:如果要清除整张表的数据,有以下两个方法:

-- 清空全部数据,不写日志,不可恢复,速度极快
truncate table 表名; -- 清空全部数据,写日志,数据可恢复,速度慢
delete from 表名

     3.3 修改数据(改)

  update 命令修改数据:

mysql> update PEOPLE set name='Calvin' where name = 'Garvey';
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0

  查询PEOPLE表内容:

mysql> select * from PEOPLE;
+----+--------+-----+---------------------+
| ID | NAME | AGE | BIRTHDAY |
+----+--------+-----+---------------------+
| 1 | Anny | 22 | 1992-05-22 00:00:00 |
| 2 | Calvin | 23 | 1991-05-22 00:00:00 |
| 4 | Nick | 24 | 1990-05-22 00:00:00 |
| 5 | Rick | 24 | 1991-05-22 00:00:00 |
+----+--------+-----+---------------------+
4 rows in set (0.00 sec)

  名为“Garvey”的记录已经修改为“Calvin”。

   3.4 查询数据(查)

  select 命令查询数据,最简单的就是查询表的所有数据,也就是我们最初使用到的那条命令:

mysql> select * from PEOPLE;
+----+--------+-----+---------------------+
| ID | NAME | AGE | BIRTHDAY |
+----+--------+-----+---------------------+
| 1 | Anny | 22 | 1992-05-22 00:00:00 |
| 2 | Calvin | 23 | 1991-05-22 00:00:00 |
| 4 | Nick | 24 | 1990-05-22 00:00:00 |
| 5 | Rick | 24 | 1991-05-22 00:00:00 |
+----+--------+-----+---------------------+
4 rows in set (0.00 sec)

  格式:select * from <表名>,*代表所有字段。

  查询数据时也可指定显示的(列)字段:

mysql> select NAME, AGE, BIRTHDAY from PEOPLE;
+--------+-----+---------------------+
| NAME | AGE | BIRTHDAY |
+--------+-----+---------------------+
| Anny | 22 | 1992-05-22 00:00:00 |
| Calvin | 23 | 1991-05-22 00:00:00 |
| Nick | 24 | 1990-05-22 00:00:00 |
| Rick | 24 | 1991-05-22 00:00:00 |
+--------+-----+---------------------+
4 rows in set (0.00 sec)

  格式:select <字段名,字段名,...> from <表名>。

  select查询命令还有很多的高级用法,比如用来查找不重复(distinct)的数据,使数据按条件排序(order by),按查询条件显示数据(where)等等。这些都会在下一篇文章作重点介绍,请大家继续留意我的博客,谢谢。

  4、管理视图

   4.1 创建视图

  视图是从数据库里导出一个或多个表的虚拟表,是用来方便用户对数据的操作。

mysql> CREATE VIEW PEOPLE_VIEW (
-> NAME, AGE)
-> AS SELECT NAME, AGE FROM PEOPLE;

  创建成功后查看视图。

PEOPLE          PEOPLE.AGE      PEOPLE.BIRTHDAY PEOPLE.ID       PEOPLE.NAME
mysql> SELECT * FROM PEOPLE_VIEW
-> ;
+--------+-----+
| NAME | AGE |
+--------+-----+
| Anny | 22 |
| Calvin | 23 |
| Nick | 24 |
| Rick | 24 |
+--------+-----+
4 rows in set (0.00 sec)

  我们也可以使用 DESC 命令查看视图的结构。

mysql> DESC PEOPLE_VIEW;
+-------+---------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| ID | int(11) | NO | | 0 | |
+-------+---------+------+-----+---------+-------+
1 row in set (0.01 sec)

   4.2 替换视图

  创建或替换原有视图。

mysql> CREATE OR REPLACE VIEW PEOPLE_VIEW(PEOPLE_ID,PEOPLE_NAME,PEOPLE_AGE) AS SELECT ID,NAME,AGE FROM PEOPLE;
Query OK, 0 rows affected (0.00 sec)

  创建或替换后查看视图。

mysql> SELECT * FROM PEOPLE_VIEW;
+-----------+-------------+------------+
| PEOPLE_ID | PEOPLE_NAME | PEOPLE_AGE |
+-----------+-------------+------------+
| 1 | Anny | 22 |
| 2 | Calvin | 23 |
| 4 | Nick | 24 |
| 5 | Rick | 24 |
+-----------+-------------+------------+
4 rows in set (0.00 sec)

   4.3 操作视图

  当视图数据有变化时(增、删、改),真实的表数据也会随着改变。也就是说,对视图的操作就是对表的数据,所以我们可以把视图当作表。

  例:往视图插入一条数据。

mysql> INSERT INTO PEOPLE_VIEW VALUES(NULL, 'Kerry', '33');
Query OK, 1 row affected (0.00 sec)

  插入数据成功后查看视图。

mysql> SELECT * FROM PEOPLE_VIEW ;
+-----------+-------------+------------+
| PEOPLE_ID | PEOPLE_NAME | PEOPLE_AGE |
+-----------+-------------+------------+
| 1 | Anny | 22 |
| 2 | Calvin | 23 |
| 4 | Nick | 24 |
| 5 | Rick | 24 |
| 6 | Kerry | 33 |
+-----------+-------------+------------+
5 rows in set (0.00 sec)

  可以在视图上看到我们刚刚插入的数据,现在我们就来验证一下真实的表是否也会作出变化。

mysql> SELECT * FROM PEOPLE;
+----+--------+-----+---------------------+
| ID | NAME | AGE | BIRTHDAY |
+----+--------+-----+---------------------+
| 1 | Anny | 22 | 1992-05-22 00:00:00 |
| 2 | Calvin | 23 | 1991-05-22 00:00:00 |
| 4 | Nick | 24 | 1990-05-22 00:00:00 |
| 5 | Rick | 24 | 1991-05-22 00:00:00 |
| 6 | Kerry | 33 | NULL |
+----+--------+-----+---------------------+
5 rows in set (0.00 sec)

  可见,真实的表数据也已经有所改变,刚刚往视图里插入的那一条数据存在于真实表中,真理便是:对视图的操作就是对表的数据。

   4.4 删除视图

mysql> DROP VIEW PEOPLE_VIEW;
Query OK, 0 rows affected (0.00 sec)