SQL语句之DWL、DCL语句
短信预约 -IT技能 免费直播动态提醒
SQL语句之DWL、DCL语句
===============================================================================
概述：
本章将主要介绍SQL语句中的DWL和DCL简单语句的使用方法，具体内容如下：
DWL语句的INSERT（增），DELETE（删），UPDATE（改），SELECT（查）
SELECT单表查询语句详解；
·SELECT语句的执行流程：
·字段可以使用别名
·WHERE子句：
·GROUP BY,分组
·聚合函数
·HAVING,对分组聚合后的结果进行条件过滤
DCL语句的简单使用；
·GRANT（授权）, REVOKE（回收权限）
===============================================================================
SQL语句之DWL语句
---INSERT，SELECT，DELETE，UPDATE
1.INSERT 增加插入数据
★语法：
INSERT [INTO] tbl_name [(col_name,...)] {VALUES | VALUE} ({expr | DEFAULT},...),(...),...
演示：
MariaDB [mydb]> desc tbl1;
+---------+----------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------+----------------------+------+-----+---------+----------------+
| id | smallint(5) unsigned | NO | PRI | NULL | auto_increment |
| name | char(30) | NO | MUL | NULL | |
| age | tinyint(3) unsigned | YES | | NULL | |
| ClassID | tinyint(3) unsigned | NO | | NULL | |
| gender | enum('F','M') | YES | | M | |
+---------+----------------------+------+-----+---------+----------------+
5 rows in set (0.01 sec)
MariaDB [mydb]> insert into tbl1 (name,ClassID) value ('tom',1); # 新增一个叫tom在1
班的同学
Query OK, 1 row affected (0.02 sec)
MariaDB [mydb]> select * from tbl1; # 查看如下：
+----+------+------+---------+--------+
| id | name | age | ClassID | gender |
+----+------+------+---------+--------+
| 1 | tom | NULL | 1 | M |
+----+------+------+---------+--------+
1 row in set (0.00 sec)
MariaDB [mydb]> insert into tbl1 (name,ClassID) value ('tao',1),('xiu',2); # 可以一次增加多个
Query OK, 2 rows affected (0.04 sec)
Records: 2 Duplicates: 0 Warnings: 0
MariaDB [mydb]> select * from tbl1;
+----+------+------+---------+--------+
| id | name | age | ClassID | gender |
+----+------+------+---------+--------+
| 1 | tom | NULL | 1 | M |
| 2 | tao | NULL | 1 | M |
| 3 | xiu | NULL | 2 | M |
+----+------+------+---------+--------+
3 rows in set (0.00 sec)
MariaDB [mydb]> insert into tbl1 value (4,'wang',25,5,default); # 直接指定值增加，但是每个字段都必须有值
Query OK, 1 row affected (0.02 sec)
MariaDB [mydb]> select * from tbl1;
+----+------+------+---------+--------+
| id | name | age | ClassID | gender |
+----+------+------+---------+--------+
| 1 | tom | NULL | 1 | M |
| 2 | tao | NULL | 1 | M |
| 3 | xiu | NULL | 2 | M |
| 4 | wang | 25 | 5 | M |
+----+------+------+---------+--------+
4 rows in set (0.00 sec) 2.DELETE 删除数据
★语法：
☉DELETE FROM tbl_name
[WHERE where_condition]
演示：
MariaDB [mydb]> select * from tbl1;
+----+------+------+---------+--------+
| id | name | age | ClassID | gender |
+----+------+------+---------+--------+
| 1 | tom | NULL | 1 | M |
| 2 | tao | NULL | 1 | M |
| 3 | xiu | NULL | 2 | M |
| 4 | wang | 25 | 5 | M |
+----+------+------+---------+--------+
4 rows in set (0.00 sec)
MariaDB [mydb]> delete from tbl1 where ClassID = 5; # 删除ClassID为5的行
Query OK, 1 row affected (0.00 sec)
MariaDB [mydb]> select * from tbl1;
+----+------+------+---------+--------+
| id | name | age | ClassID | gender |
+----+------+------+---------+--------+
| 1 | tom | NULL | 1 | M |
| 2 | tao | NULL | 1 | M |
| 3 | xiu | NULL | 2 | M |
+----+------+------+---------+--------+
3 rows in set (0.00 sec) 3.UPDATE 修改数据
★语法：
☉UPDATE table_reference SET col_name1={expr1|DEFAULT} [, col_name2={expr2|DEFAULT}] ...
[WHERE where_condition]
演示：
MariaDB [mydb]> update tbl1 set age=18 where id=2; # 修改id=2的行age=18
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
MariaDB [mydb]> select * from tbl1;
+----+------+------+---------+--------+
| id | name | age | ClassID | gender |
+----+------+------+---------+--------+
| 1 | tom | NULL | 1 | M |
| 2 | tao | 18 | 1 | M |
| 3 | xiu | NULL | 2 | M |
+----+------+------+---------+--------+
3 rows in set (0.00 sec)
MariaDB [mydb]> update tbl1 set age=18,ClassID=3 where id=1; #修改id=2的行age=18，ClassID=3
Query OK, 1 row affected (0.05 sec)
Rows matched: 1 Changed: 1 Warnings: 0
MariaDB [mydb]> select * from tbl1;
+----+------+------+---------+--------+
| id | name | age | ClassID | gender |
+----+------+------+---------+--------+
| 1 | tom | 18 | 3 | M |
| 2 | tao | 18 | 1 | M |
| 3 | xiu | NULL | 2 | M |
+----+------+------+---------+--------+
3 rows in set (0.00 sec) 4.SELECT：查询
★Query Cache：缓存查询的执行结果；
☉key：查询语句的hash值；
☉value：查询语句的执行结果；
☉SQL语句的编写方式：
要养成同一种风格书写方式，要大写都大写，要小写都小写，方便查询缓存；
★查询执行路径：
请求-->查询缓存
请求-->查询缓存-->解析器-->预处理器-->优化器-->查询执行引擎-->存储引擎-->缓存-->响应
★SELECT语句的执行流程：
FROM --> WHERE（条件过滤）--> Group By（分组聚合）--> Having（对分组统计再加限制条件）--> Order BY（排序）--> SELECT --> Limit（限定数据处理后显示的行数）
select是用来挑选字段的，而where是用来挑选行的；mysql关系型数据库为一个行级数据库，所有数据先取行，然后对行过滤之后保留关键字段，
★单表查询：
☉SELECT
☉语句用法：
◆SELECT * FROM tbl_name;
查询一个指定表的所有行（生产环境中一定不可用）；
◆SELECT col1, col2, ... FROM tble_name；
查询指定表符合条件的字段，（字段为所有行的字段）
字段别名：col1 AS ALIAS
◆SELECT col1, col2, ... FROM tble_name WHERE clause；
以指定条件过滤行之后再挑选字段
◆SELECT col1, col2, ... FROM tble_name [WHERE clause] GROUP BY col_name [HAVING clause]；
以指定的字段进行分组，分完组之后聚合，然后对聚合后的结果使用having子句进行过滤；
◆SELECT col1, ... FROM tbl1_name [WEHRE CLAUSE] ORDER BY col1, col2, ... [ASC|DESC]
查询后以指定字段排序（默认为升序）
★选项：
☉DISTINCT：数据去重；
☉SQL_CACHE：显式指定缓存查询语句的结果；
☉SQL_NO_CACHE：显式指定不缓存查询语句的结果；
☉query_cache_type服务器变量有三个值：
ON：启用；
SQL_NO_CACHE：不缓存；默认符合缓存条件都缓存；
OFF：关闭；
DEMAND：按需缓存；
SQL_CACHE：缓存；默认不缓存；
☉字段可以使用别名 ：
col1 AS alias1, col2 AS alias2, ...
☉WHERE子句：指明过滤条件以实现“选择”功能；
◆过滤条件：布尔型表达式；
◆[WHERE where_condition]
算术操作符：+, -, *, /, %
比较操作符：=, <>, !=, <=>, >, >=, <, <=
·IS NULL， IS NOT NULL
·区间：BETWEEN min AND max
·IN(list)：列表；
·LIKE 'PATTERN'：模糊比较
通配符：
%：任意长度的任意字符；
_；匹配任意单个字符；
·RLIKE或REGEXP
逻辑操作符：AND， OR， NOT， XOR
☉GROUP BY：
根据指定的字段把查询的结果进行“分组”以用于“聚合”运算；
avg(), max(), min(), sum(), count()
☉HAVING：
对分组聚合后的结果进行条件过滤；
☉ORDER BY：根据指定的字段把查询的结果进行排序；
升序：ASC
降序：DESC
☉LIMIT：对输出结果进行数量限制
[LIMIT {[offset,] row_count | row_count OFFSET offset}]
演示：
1.select查询指定的字段和行
MariaDB [mydb]> select * from tbl1; # 查询指定表的所有行
+----+------+------+---------+--------+
| id | name | age | ClassID | gender |
+----+------+------+---------+--------+
| 1 | tom | NULL | 1 | M |
| 2 | tao | NULL | 1 | M |
| 3 | xiu | NULL | 2 | M |
| 4 | wang | 25 | 5 | M |
+----+------+------+---------+--------+
4 rows in set (0.00 sec)
MariaDB [mydb]> select name,gender from tbl1; # 查询指定表符合条件的字段
+------+--------+
| name | gender |
+------+--------+
| tom | M |
| tao | M |
| xiu | M |
| wang | M |
+------+--------+
4 rows in set (0.00 sec)
MariaDB [mydb]> select name AS StuName,gender from tbl1; # 定义字段别名
+---------+--------+
| StuName | gender |
+---------+--------+
| tom | M |
| tao | M |
| xiu | M |
| wang | M |
+---------+--------+
4 rows in set (0.00 sec)
MariaDB [mydb]>2.where 子句演示：Classe
MariaDB [mydb]> select * from tbl1;
+----+------+------+---------+--------+
| id | name | age | ClassID | gender |
+----+------+------+---------+--------+
| 1 | tom | NULL | 1 | M |
| 2 | tao | NULL | 1 | M |
| 3 | xiu | NULL | 2 | M |
| 4 | wang | 25 | 5 | M |
+----+------+------+---------+--------+
4 rows in set (0.00 sec)
MariaDB [mydb]> select * from tbl1 where ClassID > 2; # 查询ClassID大于2的
+----+------+------+---------+--------+
| id | name | age | ClassID | gender |
+----+------+------+---------+--------+
| 4 | wang | 25 | 5 | M |
+----+------+------+---------+--------+
1 row in set (0.00 sec)
MariaDB [mydb]> select * from tbl1 where ClassID >= 2 and ClassID <=5; # 组合条件查询班号大于2小于5的
+----+------+------+---------+--------+
| id | name | age | ClassID | gender |
+----+------+------+---------+--------+
| 3 | xiu | NULL | 2 | M |
| 4 | wang | 25 | 5 | M |
+----+------+------+---------+--------+
2 rows in set (0.00 sec)
MariaDB [mydb]> select * from tbl1 where ClassID between 2 and 5; # 同上，另一种写法between...and..
+----+------+------+---------+--------+
| id | name | age | ClassID | gender |
+----+------+------+---------+--------+
| 3 | xiu | NULL | 2 | M |
| 4 | wang | 25 | 5 | M |
+----+------+------+---------+--------+
2 rows in set (0.00 sec)
MariaDB [mydb]> select name from tbl1 where name like '%o%'; # 匹配name中带o的名字
+------+
| name |
+------+
| tom |
| tao |
+------+
2 rows in set (0.01 sec)
MariaDB [mydb]> select name from tbl1 where name like '%u'; # 匹配name中以u结尾的名字
+------+
| name |
+------+
| xiu |
+------+
1 row in set (0.00 sec)
MariaDB [mydb]> select name from tbl1 where name rlike '^.*o.*$';# 正则表达式匹配名字中带o的
+------+
| name |
+------+
| tom |
| tao |
+------+
2 rows in set (0.00 sec)
MariaDB [mydb]> select name,ClassID from tbl1 where ClassID in (1,2); # 在给定列表元素中查找
+------+---------+
| name | ClassID |
+------+---------+
| tom | 1 |
| tao | 1 |
| xiu | 2 |
+------+---------+
3 rows in set (0.00 sec)3.排序
MariaDB [mydb]> select * from tbl1;
+----+------+------+---------+--------+
| id | name | age | ClassID | gender |
+----+------+------+---------+--------+
| 1 | tom | NULL | 1 | M |
| 2 | tao | NULL | 1 | M |
| 3 | xiu | NULL | 2 | M |
| 4 | wang | 25 | 5 | M |
+----+------+------+---------+--------+
4 rows in set (0.00 sec)
MariaDB [mydb]> select * from tbl1 order by ClassID; # 按 ClassID 升序排序
+----+------+------+---------+--------+
| id | name | age | ClassID | gender |
+----+------+------+---------+--------+
| 1 | tom | NULL | 1 | M |
| 2 | tao | NULL | 1 | M |
| 3 | xiu | NULL | 2 | M |
| 4 | wang | 25 | 5 | M |
+----+------+------+---------+--------+
4 rows in set (0.01 sec)
MariaDB [mydb]> select * from tbl1 order by ClassID,name; # 如果ClassID相同就按name升序排列
+----+------+------+---------+--------+
| id | name | age | ClassID | gender |
+----+------+------+---------+--------+
| 2 | tao | NULL | 1 | M |
| 1 | tom | NULL | 1 | M |
| 3 | xiu | NULL | 2 | M |
| 4 | wang | 25 | 5 | M |
+----+------+------+---------+--------+
4 rows in set (0.03 sec)
MariaDB [mydb]> select * from tbl1 order by ClassID,name DESC;# 如果ClassID相同就按name降序排列
+----+------+------+---------+--------+
| id | name | age | ClassID | gender |
+----+------+------+---------+--------+
| 1 | tom | NULL | 1 | M |
| 2 | tao | NULL | 1 | M |
| 3 | xiu | NULL | 2 | M |
| 4 | wang | 25 | 5 | M |
+----+------+------+---------+--------+
4 rows in set (0.02 sec)
MariaDB [mydb]> select * from tbl1 order by ClassID DESC; # 按ClassID降序排列
+----+------+------+---------+--------+
| id | name | age | ClassID | gender |
+----+------+------+---------+--------+
| 4 | wang | 25 | 5 | M |
| 3 | xiu | NULL | 2 | M |
| 1 | tom | NULL | 1 | M |
| 2 | tao | NULL | 1 | M |
+----+------+------+---------+--------+
4 rows in set (0.00 sec)
# 按ClassID降序排列，如果相同就按name降序排列
MariaDB [mydb]> select * from tbl1 order by ClassID DESC,name DESC;
+----+------+------+---------+--------+
| id | name | age | ClassID | gender |
+----+------+------+---------+--------+
| 4 | wang | 25 | 5 | M |
| 3 | xiu | NULL | 2 | M |
| 2 | tao | NULL | 1 | M |
| 1 | tom | NULL | 1 | M |
+----+------+------+---------+--------+
4 rows in set (0.00 sec)--------------------------------------------------------------------------------
1.select挑选字段和where挑选行
MariaDB [testdb]> show tables;
+------------------+
| Tables_in_testdb |
+------------------+
| tbl1 |
| tbl2 |
+------------------+
2 rows in set (0.00 sec)
MariaDB [testdb]> select id from tbl2; # select仅挑选字段
+------+
| id |
+------+
| 1 |
| 2 |
| 3 |
+------+
3 rows in set (0.00 sec)
MariaDB [testdb]> select * from tbl2; # 显示所有的字段
+------+------+------+
| id | name | age |
+------+------+------+
| 1 | tom | 21 |
| 2 | tao | 15 |
| 3 | jing | 22 |
+------+------+------+
3 rows in set (0.00 sec)
MariaDB [testdb]> select * from tbl2 where age>=20; # where挑选行
+------+------+------+
| id | name | age |
+------+------+------+
| 1 | tom | 21 |
| 3 | jing | 22 |
+------+------+------+
2 rows in set (0.00 sec)
MariaDB [testdb]> select name,age from tbl2 where age>=20; # 即挑选字段又挑选行
+------+------+
| name | age |
+------+------+
| tom | 21 |
| jing | 22 |
+------+------+2.对挑选出的数据分组 Group By，分组的目的在于聚合
MariaDB [testdb]> alter table tbl2 add gender enum('F','M'); #增加一个gender字段
Query OK, 3 rows affected (0.03 sec)
Records: 3 Duplicates: 0 Warnings: 0
MariaDB [testdb]> select * from tbl2;
+------+------+------+--------+
| id | name | age | gender |
+------+------+------+--------+
| 1 | tom | 21 | NULL |
| 2 | tao | 15 | NULL |
| 3 | jing | 22 | NULL |
+------+------+------+--------+
3 rows in set (0.00 sec)
MariaDB [testdb]> update tbl2 set gender='M' where id=1; # 设定其值
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
MariaDB [testdb]> update tbl2 set gender='M' where id=2;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
MariaDB [testdb]> update tbl2 set gender='F' where id=3;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1 Changed: 1 Warnings: 0
MariaDB [testdb]> select * from tbl2;
+------+------+------+--------+
| id | name | age | gender |
+------+------+------+--------+
| 1 | tom | 21 | M |
| 2 | tao | 15 | M |
| 3 | jing | 22 | F |
+------+------+------+--------+
3 rows in set (0.00 sec)
MariaDB [testdb]> select * from tbl2 group by gender; # 按性别对tbl2进行分组（有几个值就分多少组）
+------+------+------+--------+
| id | name | age | gender |
+------+------+------+--------+
| 3 | jing | 22 | F |
| 1 | tom | 21 | M |
+------+------+------+--------+
2 rows in set (0.01 sec)
MariaDB [testdb]> select avg(age),gender from tbl2 group by gender; # 对各分组求其平均值
+----------+--------+
| avg(age) | gender |
+----------+--------+
| 22.0000 | F |
| 18.0000 | M |
+----------+--------+
2 rows in set (0.00 sec)
MariaDB [testdb]> select sum(age),gender from tbl2 group by gender; # 对各分组求和
+----------+--------+
| sum(age) | gender |
+----------+--------+
| 22 | F |
| 36 | M |
+----------+--------+
2 rows in set (0.00 sec)
MariaDB [testdb]> select avg(age) as avg_age,gender from tbl2 group by gender; #对avg_age定义别名
+---------+--------+
| avg_age | gender |
+---------+--------+
| 22.0000 | F |
| 18.0000 | M |
+---------+--------+
2 rows in set (0.01 sec)3.对聚合后的结果指明过滤条件HAVING
MariaDB [testdb]> select avg(age) as avg_age,gender from tbl2 group by gender having avg_age >= 20;
+---------+--------+
| avg_age | gender |
+---------+--------+
| 22.0000 | F |
+---------+--------+
1 row in set (0.01 sec)4.数据去重
MariaDB [testdb]> select gender from tbl2;
+--------+
| gender |
+--------+
| M |
| M |
| F |
+--------+
3 rows in set (0.00 sec)
MariaDB [testdb]> select distinct gender from tbl2; # 去重
+--------+
| gender |
+--------+
| M |
| F |
+--------+
2 rows in set (0.00 sec)
MariaDB [testdb]> SHOW VARIABLES LIKE '%cache%'; # 和缓存cache相关的参数
+-------------------------------+----------------------+
| Variable_name | Value |
+-------------------------------+----------------------+
| aria_pagecache_age_threshold | 300 |
| aria_pagecache_buffer_size | 134217728 |
| aria_pagecache_division_limit | 100 |
| binlog_cache_size | 32768 |
| binlog_stmt_cache_size | 32768 |
| have_query_cache | YES |
| join_cache_level | 2 |
| key_cache_age_threshold | 300 |
| key_cache_block_size | 1024 |
| key_cache_division_limit | 100 |
| key_cache_segments | 0 |
| max_binlog_cache_size | 18446744073709547520 |
| max_binlog_stmt_cache_size | 18446744073709547520 |
| metadata_locks_cache_size | 1024 |
| query_cache_limit | 1048576 |
| query_cache_min_res_unit | 4096 |
| query_cache_size | 0 | # 为0，没有缓存空间
| query_cache_strip_comments | OFF |
| query_cache_type | ON | # 缓存为开启状态
| query_cache_wlock_invalidate | OFF |
| stored_program_cache | 256 |
| table_definition_cache | 400 |
| table_open_cache | 400 |
| thread_cache_size | 0 |
+-------------------------------+----------------------+
24 rows in set (0.00 sec)=============================================================================
SQL语句之DCL语句
GRANT（授权）, REVOKE（回收权限）
命令演示：
1.授权一个用户仅允许本地登录
[root@centos7 bbs]# mysql -p134296 # 不指定用户，默认就是使用root用户登录mysql
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MariaDB connection id is 6
Server version: 5.5.44-MariaDB MariaDB Server
Copyright (c) 2000, 2015, Oracle, MariaDB Corporation Ab and others.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
MariaDB [(none)]> CREATE DATABASE ultrax; # 创建数据库
Query OK, 1 row affected (0.00 sec)
# 授权用户名为ultraxuser,仅允许本地登录访问ultrax数据库，密码为134296
MariaDB [(none)]> GRANT ALL ON ultrax.* TO 'ultraxuser'@'localhost' IDENTIFIED BY '134296';
Query OK, 0 rows affected (0.00 sec)
MariaDB [(none)]> FLUSH PRIVILEGES; # 重载权限表
Query OK, 0 rows affected (0.00 sec)
MariaDB [(none)]>2.授权一个可远程登录的用户和主机
[root@centos7 ~]# mysql
Welcome to the MariaDB monitor. Commands end with ; or \g.
Your MariaDB connection id is 2
Server version: 5.5.44-MariaDB MariaDB Server
Copyright (c) 2000, 2015, Oracle, MariaDB Corporation Ab and others.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
# 授权的用户为test，主机为10.1网段中的任何主机，允许访问所有的数据库和表，密码为testpass
MariaDB [(none)]> GRANT all ON *.* TO 'test'@'10.1.%.%' IDENTIFIED BY 'testpass';
Query OK, 0 rows affected (0.01 sec)
MariaDB [(none)]> FLUSH PRIVILEGES;
Query OK, 0 rows affected (0.00 sec)
mysql> create database mydb; # 创建一个数据库
Query OK, 1 row affected (0.00 sec)
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mydb |
| mysql |
| performance_schema |
| test |
+--------------------+
5 rows in set (0.01 sec)
MariaDB [(none)]> exit
Bye免责声明：
① 本站未注明“稿件来源”的信息均来自网络整理。其文字、图片和音视频稿件的所属权归原作者所有。本站收集整理出于非商业性的教育和科研之目的，并不意味着本站赞同其观点或证实其内容的真实性。仅作为临时的测试数据，供内部测试之用。本站并未授权任何人以任何方式主动获取本站任何信息。
② 本站未注明“稿件来源”的临时测试数据将在测试完成后最终做删除处理。有问题或投稿请发送至: 邮箱/279061341@qq.com QQ/279061341
![[mysql]mysql8修改root密码](https://static.528045.com/imgs/7.jpg?imageMogr2/format/webp/blur/1x0/quality/35)
