ip2region -- 查询IP地址

# 1.可以通过 as 给表起别名 
select students.id,students.name,students.gender from students;
select s.id,s.name,s.gender from students as s;

# 2. distinct可以去除重复数据行
select distinct name, gender from students;

# 3.where条件查询语法格式如下:
select * from 表名 where 条件;
eg:
select * from students where id = 1;

# 4.比较运算符查询
    等于: =
    大于: >
    大于等于: >=
    小于: <
    小于等于: <=
    不等于: != 或 <>
    
查询编号大于3的学生:
select * from students where id > 3;
查询编号不大于4的学生:
select * from students where id <= 4;
查询姓名不是“小明”的学生:
select * from students where name != '小明';

# 5.逻辑运算符查询

查询编号大于3的女同学:
select * from students where id > 3 and gender=0;
查询编号小于4或没被删除的学生:
select * from students where id < 4 or is_delete=0;
查询年龄不在10岁到15岁之间的学生:
select * from students where not (age >= 10 and age <= 15);

# 6.模糊查询
like是模糊查询关键字
%表示任意多个任意字符
_表示一个任意字符

查询姓黄的学生:
select * from students where name like '黄%';
查询姓黄并且“名”是一个字的学生:
select * from students where name like '黄_';
查询姓黄或叫靖的学生:
select * from students where name like '黄%' or name like '%靖';

# 7.范围查询
between .. and .. 表示在一个连续的范围内查询
in 表示在一个非连续的范围内查询

查询编号为3至8的学生:
select * from students where id between 3 and 8;
查询编号不是3至8的男生:
select * from students where (not id between 3 and 8) and gender='男';

# 8.空判断查询
判断为空使用: is null
判断非空使用: is not null

查询没有填写身高的学生:
select * from students where height is null;

# 9.排序查询语法
select * from 表名 order by 列1 asc|desc [,列2 asc|desc,...]
说明：
asc从小到大排列，即升序
desc从大到小排序，即降序
默认按照列值从小到大排序（即asc关键字）

查询未删除男生信息，按学号降序:
select * from students where gender=1 and is_delete=0 order by id desc;
显示所有的学生信息，先按照年龄从大-->小排序，当年龄相同时 按照身高从高-->矮排序
select * from students  order by age desc,height desc;

# 10.分页查询的语法
select * from 表名 limit start,count

查询前3行男生信息
select * from students where gender=1 limit 0,3;
简写
select * from students where gender=1 limit 3;

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