mysql 常用命令练习

管理表格

创建一个包含三列的新表
CREATETABLEproducts(
    id    INT,
    name  VARCHAR(255)NOTNULL,
    price INTDEFAULT0,PRIMARYKEY(id)// 自增);
从数据库中删除表
DROPTABLE product;
向表中添加新列
ALTERTABLE product ADD column_name VARCHAR(255)DEFAULT'';
从表中删除列c
ALTERTABLE product DROPCOLUMN column_name
添加约束
ALTERTABLE product ADD constraint check_price_positive check(age>=0);
删除约束
ALTERTABLE product DROP constraint check_price_positive;
将表从product重命名为products
ALTERTABLE product RENAMETO products;
将列names重命名为name
ALTERTABLE products  CHANGE names name INT将列name的数据类型改为varchart(255)ALTERTABLE products MODIFY name VARCHAR(255);
删除表中的所有数据
TRUNCATETABLE products

从表中查询数据

从表中查询列c1、c2中的数据
select value,set_time from sys_config
查询表中的所有行和列
select * from sys_config sc 
查询数据并使用条件筛选行
select value,set_time from sys_config sc WHERE value =100
select value,set_time from sys_config sc WHERE value <>100
select value,set_time from sys_config sc WHERE value like '%F%'
select value,set_time from sys_config sc WHERE value not like '%F%'
select value,set_time from sys_config sc WHERE value ISNULL
select value,set_time from sys_config sc WHERE value is not  NULL
select value,set_time from sys_config sc WHERE value BETWEEN50AND200
select value,set_time from sys_config sc WHERE value IN(64,65,66)
select value,set_time from sys_config sc WHERE value not IN(64,65,66)查询表中的不同行(去重)
select distinct  value,set_time, from sys_config sc
按升序或降序对结果集排序
select * from sys_config sc ORDERBY set_time ASC
select * from sys_config sc ORDERBY set_time DESC跳过行的偏移并返回下n行(分页)SELECT*FROM sys_config  sc ORDERBY value limit  10OFFSET0
使用聚合函数对行进行分组
SELECT value,MAX(set_time),count(*)FROM sys_config  sc GROUPBY value,set_time
SELECT value,avg(set_time)FROM sys_config  sc GROUPBY value,set_time
使用HAVING子句筛选组(过滤)SELECT value,avg(set_time)FROM sys_config  sc GROUPBY value,set_time having value <>100

从多个表查询

内部连接 t1 和 t2
SELECT n.*,a.ages FROM names n INNERJOIN ages a on n.name = a.name
左连接t1和t1
SELECT n.*,a.ages FROM names n left JOIN ages a on n.name = a.name

修改数据

在表格中插入一行
INSERTINTOsys_config(variable,value,set_time,set_by)VALUES(1,2,'2023-07-11 18:29:24',4);
在表格中插入多行
INSERTINTOsys_config(variable,value,set_time,set_by)VALUES(15,2,'2023-07-11 18:29:24',4),(5,6,'2023-07-11 18:29:24',7);将行从t2插入t1(跨表)INSERTINTOnames(id,name,num)SELECT id,name,1AS num FROM ages;
更新列c1中所有行的新值
UPDATE names SET num =1;
更新列c1、c2中与条件匹配的值
UPDATE names SET num =11 where name =2;
删除表中的行子集
DELETEFROM names WHERE id =1;

sql变量类型

链接