SQL语句之DWL语句
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概述：
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SQL语句之DWL语句
INSERT，SELECT，DELETE，UPDATE
1.INSERT 增加数据
★语法：
- INSERT [INTO] tbl_name [(col_name,...)] {VALUES | VALUE} ({expr | DEFAULT},...),(...),...
命令演示：
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 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]
示例：
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]
示例：
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：
★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）
☉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；
☉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：
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]>
where 子句演示：
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]> 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)
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）
命令示例：
1）授权一个用户仅允许本地登录
[[email protected] 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
[[email protected] ~]# 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
时间： 2024-11-09 15:26:32