TIP
limit 1,10 就是从第一条开始,取10 条users 的记录
收到客户端{pageNo:1,pagesize:10}
select * from table limit (pageNo-1)*pageSize, pageSize;
收到客户端{pageNo:5,pageSize:30}
select * from table limit (pageNo-1)*pageSize,pageSize;
内部联结 JOIN
内部联结又称为等值联结,它基于两个表之间的相等测试。
SELECT
vend_name,
prod_name,
prod_price
FROM vendors v
JOIN products p
USING (vend_id)
ORDER BY vend_name, prod_name
-- 自联结
SELECT
p1.prod_id,
p1.prod_name
FROM products p1
JOIN products p2
ON p1.vend_id = p2.vend_id
AND p2.prod_id = 'DTNTR'
外部联结
SELECT
c.cust_id,
o.order_num
FROM customers c
LEFT JOIN orders o
ON c.cust_id = o.cust_id
聚集函数
SELECT
c.cust_name,
c.cust_id,
count(o.order_num) as num_ord
FROM customers c
LEFT JOIN orders o
ON c.cust_id = o.cust_id
GROUP BY c.cust_id
UNION
在某种程度上 UNION 可以大幅简化 WHERE 子句。
UNION 中每个查询必须包含相同的列、表达式或聚集函数。
-- 指定 ALL 不会取消重复的行
SELECT
vend_id,
prod_id,
prod_price
FROM products
WHERE prod_price <= 5
UNION ALL
SELECT
vend_id,
prod_id,
prod_price
FROM products
WHERE vend_id IN (1001, 1002)
INSERT
指令 | 已存在 | 不存在 | 举例 |
---|---|---|---|
insert | 报错 | 插入 | insert into names(name, age) values(“小明”, 23); |
insert ignore | 忽略 | 插入 | insert ignore into names(name, age) values(“小明”, 24); |
replace | 替换 | 插入 | replace into names(name, age) values(“小明”, 25); |
插入数据最好指定列名,可跳过默认取默认值的列且可更改顺序。
多行数据以 ,
分隔。
INSERT INTO customers
(cust_name, cust_address, cust_city, cust_state, cust_zip, cust_country)
VALUES
('Pep E. LaPew', '100 Main Street', 'Los Angeles', 'CA', '90046', 'USA'),
('M. Martian', '42 Galaxy', 'New York', 'NY', '11213', 'USA')
UPDATE
更新语句由三部分组成:
- 要更新的表
- 列名和它们的新值
- 确定要更新行的过滤条件
UPDATE customers
SET
cust_name = 'The Fudd',
cust_email = 'elmer@fudd.com'
WHERE cust_id = 10005
DELETE
注意检查 WHERE 有没有使用。
DELETE FROM customers
WHERE cust_id = 10006
Mysql常用命令
数据定义语句(DDL)
数据库操作
- 登录数据库:mysql -uroot -proot
- 创建数据库:create database test
- 查看所有数据库:show databases
- 使用数据库:use test
- 查看所有数据表:show tables
- 删除数据库:drop database test
表操作
- 创建表:create table emp(ename varchar(10),hiredate date,sal decimal(10,2),deptno int(2))
create table dept(deptno int(2),deptname varchar(10)) - 查看表的定义:desc emp
- 查看表定义(详细):show create table emp \G
- 删除表:drop table emp
- 修改表字段:alter table emp modify ename varchar(20)
- 添加表字段:alter table emp add column age int(3)
- 删除表字段:alter table emp drop column age
- 字段改名;alter table emp change age age1 int(4)
- 修改表名:alter table emp rename emp1
数据操纵语句(DML)
插入记录
- 指定名称插入:insert into emp (ename,hiredate,sal,deptno) values ('zhangsan','2018-01-01','2000',1)
- 不指定名称插入:insert into emp values ('lisi','2018-01-01','2000',1)
- 批量插入数据:insert into dept values(1,'dept1'),(2,'dept2')
修改记录
update emp set sal='4000',deptno=2 where ename='zhangsan'
删除记录
delete from emp where ename='zhangsan'
查询记录
- 查询所有记录:select * from emp
- 查询不重复的记录:select distinct deptno from emp
- 条件查询:select * from emp where deptno=1 and sal<3000
- 排序和限制:select * from emp order by deptno desc limit 2
- 聚合(查询部门人数大于1的部门编号):select deptno,count(1) from emp group by deptno having count(1) > 1
- 连接查询:select * from emp e left join dept d on e.deptno=d.deptno
- 子查询:select * from emp where deptno in (select deptno from dept)
- 记录联合:select deptno from emp union select deptno from dept
数据控制语句(DCL)
- 授予操作权限:grant select,insert on test.* to 'test'@'localhost' identified by '123'
- 收回操作权限:revoke insert on test.* from 'test'@'localhost'
其他
字符集相关
- 查看字符集:show variables like 'character%'
- 创建数据库时指定字符集:create database mall character set utf8
修改时区
- 修改mysql全局时区为北京时间,即我们所在的东8区:
set global time_zone = '+8:00'
; - 修改当前会话时区:
set time_zone = '+8:00'
- 立即生效:
flush privileges
权限相关
- 授予所有数据库的所有权限:
grant all privileges on *.* to user_name@localhost identified by '123'
- 授予所有数据库的所有权限(包括grant):
grant all privileges on *.* to user_name@localhost with grant option
- 授予SUPER PROCESS FILE权限:
grant super,process,file on *.* to user_name@localhost
- 只授予登录权限:
grant usage on *.* to user_name@localhost
- 查看账号权限:
show grants for user_name@localhost
- 修改自己的密码:
set password = password('123')
- 管理员修改他人密码:
set password for 'user_name'@'localhost' = password('123')
- 删除账号:
drop user user_name@localhost