Mtsql:常用代码Create table CeShi1(     Uid varchar(50) primary key,     Pwd varchar(50),     Name varchar(50)     Nation varchar(50),     foreign key (Nation)  references Nation（Code）   //加外键关系    //references 引用    )写查询语句需要注意：1.创建表的时候，最后一列后面不要写逗号。2.如果有多条语句一起执行，注意在语句之间加分号分隔。3.写代码所有符号都是半角的。关系型数据库：表和表之间是有关系存在的创建表的几个关键字;1.主键：primary key2.非空: not null3.自增长列：auto_increment4.外键关系：foreign key (列名)  references 表名（列名）CRUD操作：  增删改查1.添加数据：Insert into 表名 values(‘’，‘’，‘’，‘’)要求values 括号里面的值的个数要求和表里面的列数相同Insert into Info (Code,Name) values(‘’，‘’)  添加指定列的值2.修改数据：Update info set Name=’张三’ where Code = ’p001’3.删除数据：Delete from info where Code = ‘p001’4.查询数据：1.普通查询：查所有的Select *from info    #查所有数据Select Code,Name from info  #查指定列2.条件查询Select *from info where Code =’p001’  #一个条件Select *from info where Name =’张三’ and Nation =’n001’  #两个条件并的关系Select *from info where Name =’张三’ or Nation =’n001’  #两个条件或的关系3.排序查询Select *from info order by Birthday  #默认升序排列asc  若果要降序排列  descSelect *from car order by Brand,Oil desc  #多列排序4.聚合函数Select count(*) from info  #取个数Select sum(price) from car   #查询price列的和Select avg(price) from car   #查询price列的平均值Select max(price) from car   #查询 price列的最大值Select min(price) from car   #查询 price列的最小值5.分页查询Select *from car limit n,m   #跳过n条数据取m条数据 6.分组查询Select brand from car group by brand    #简单分组查询Select brand from car group by brand having count(*)>2        #查询系列里面车的数量大于2的系列7.去重查询Select distinct brand from car8.修改列名Select brand as ‘系列’ from car9.模糊查询Select *from car where name like ‘奥迪%’    # %代表任意多个字符Select *from car where name like ‘_迪%’          # _代表一个字符 10.离散查询Select *from car where code in (‘c001’,’c002’,’c003’,’c004’)Select *from car where code not in (‘c001’,’c002’,’c003’,’c004’)