18 12 06 sql 的 基本语句 查询 条件查询 逻辑运算符 模糊查询 范围查询 排序 聚合函数 分组 分页 连接查询 自关联 子查询

数据的准备 -- 创建一个数据库 create database python_test charset=utf8; -- 使用一个数据库 use python_test; -- 显示使用的当前数据是哪个? select database(); -- 创建一个数据表 -- students表 create table students( id int unsigned primary key auto_increment not null, name varchar(20) default ‘‘, age tinyint unsigned default 0, height decimal(5,2), gender enum(‘男‘,‘女‘,‘中性‘,‘保密‘) default ‘保密‘, cls_id int unsigned default 0, is_delete bit default 0 ); -- 向students表中插入数据 insert into students values (0,‘小明‘,18,180.00,2,1,0), (0,‘小月月‘,18,180.00,2,2,1), (0,‘彭于晏‘,29,185.00,1,1,0), (0,‘刘德华‘,59,175.00,1,2,1), (0,‘黄蓉‘,38,160.00,2,1,0), (0,‘凤姐‘,28,150.00,4,2,1), (0,‘王祖贤‘,18,172.00,2,1,1), (0,‘周杰伦‘,36,NULL,1,1,0), (0,‘程坤‘,27,181.00,1,2,0), (0,‘刘亦菲‘,25,166.00,2,2,0), (0,‘金星‘,33,162.00,3,3,1), (0,‘静香‘,12,180.00,2,4,0), (0,‘郭靖‘,12,170.00,1,4,0), (0,‘周杰‘,34,176.00,2,5,0); -- classes表 create table classes ( id int unsigned auto_increment primary key not null, name varchar(30) not null ); -- 向classes表中插入数据 insert into classes values (0, "python_01期"), (0, "python_02期"); -- 展示是该数据库下的所有的表 show tabes; -- 查询 -- 查询所有字段 -- select * from 表名; select * from students; select * from classes; select id, name from classes; -- 查询指定字段 -- select 列1,列2,... from 表名; select name, age from students; -- 使用 as 给字段起别名 -- select 字段 as 名字.... from 表名; select name as 姓名, age as 年龄 from students; -- select 表名.字段 .... from 表名; select students.name, students.age from students; -- 可以通过 as 给表起别名 -- select 别名.字段 .... from 表名 as 别名; select students.name, students.age from students; select s.name, s.age from students as s; -- 失败的select students.name, students.age from students as s; -- 消除重复行 -- distinct 字段 select distinct gender from students; -- 条件查询 -- 比较运算符 -- select .... from 表名 where ..... -- > -- 查询大于18岁的信息 select * from students where age>18; select id,name,gender from students where age>18; -- < -- 查询小于18岁的信息 select * from students where age<18; -- >= -- <= -- 查询小于或者等于18岁的信息 -- = -- 查询年龄为18岁的所有学生的名字 select * from students where age=18; -- != 或者 <> -- 逻辑运算符 -- and -- 18到28之间的所以学生信息 select * from students where age>18 and age<28; -- 失败select * from students where age>18 and <28; -- 18岁以上的女性 select * from students where age>18 and gender="女"; select * from students where age>18 and gender=2; -- or -- 18以上或者身高查过180(包含)以上 select * from students where age>18 or height>=180; -- not -- 不在 18岁以上的女性 这个范围内的信息 -- select * from students where not age>18 and gender=2; select * from students where not (age>18 and gender=2); -- 年龄不是小于或者等于18 并且是女性 select * from students where (not age<=18) and gender=2; -- 模糊查询 -- like -- % 替换1个或者多个 -- _ 替换1个 -- 查询姓名中 以 "小" 开始的名字 select name from students where name="小"; select name from students where name like "小%"; -- 查询姓名中 有 "小" 所有的名字 select name from students where name like "%小%"; -- 查询有2个字的名字 select name from students where name like "__"; -- 查询有3个字的名字 select name from students where name like "__"; -- 查询至少有2个字的名字 select name from students where name like "__%"; -- rlike 正则 -- 查询以 周开始的姓名 select name from students where name rlike "^周.*"; -- 查询以 周开始、伦结尾的姓名 select name from students where name rlike "^周.*伦$"; -- 范围查询 -- in (1, 3, 8)表示在一个非连续的范围内 -- 查询 年龄为18、34的姓名 select name,age from students where age=18 or age=34; select name,age from students where age=18 or age=34 or age=12; select name,age from students where age in (12, 18, 34); -- not in 不非连续的范围之内 -- 年龄不是 18、34岁之间的信息 select name,age from students where age not in (12, 18, 34); -- between ... and ...表示在一个连续的范围内 -- 查询 年龄在18到34之间的的信息 select name, age from students where age between 18 and 34; -- not between ... and ...表示不在一个连续的范围内 -- 查询 年龄不在在18到34之间的的信息 select * from students where age not between 18 and 34; select * from students where not age between 18 and 34; -- 失败的select * from students where age not (between 18 and 34); -- 空判断 -- 判空is null -- 查询身高为空的信息 select * from students where height is null; select * from students where height is NULL; select * from students where height is Null; -- 判非空is not null select * from students where height is not null; -- 排序 -- order by 字段 -- asc从小到大排列，即升序 -- desc从大到小排序，即降序 -- 查询年龄在18到34岁之间的男性，按照年龄从小到到排序 select * from students where (age between 18 and 34) and gender=1; select * from students where (age between 18 and 34) and gender=1 order by age; select * from students where (age between 18 and 34) and gender=1 order by age asc; -- 查询年龄在18到34岁之间的女性，身高从高到矮排序 select * from students where (age between 18 and 34) and gender=2 order by height desc; -- order by 多个字段 -- 查询年龄在18到34岁之间的女性，身高从高到矮排序, 如果身高相同的情况下按照年龄从小到大排序 select * from students where (age between 18 and 34) and gender=2 order by height desc,id desc; -- 查询年龄在18到34岁之间的女性，身高从高到矮排序, 如果身高相同的情况下按照年龄从小到大排序, -- 如果年龄也相同那么按照id从大到小排序 select * from students where (age between 18 and 34) and gender=2 order by height desc,age asc,id desc; -- 按照年龄从小到大、身高从高到矮的排序 select * from students order by age asc, height desc; -- 聚合函数 -- 总数 -- count -- 查询男性有多少人，女性有多少人 select * from students where gender=1; select count(*) from students where gender=1; select count(*) as 男性人数 from students where gender=1; select count(*) as 女性人数 from students where gender=2; -- 最大值 -- max -- 查询最大的年龄 select age from students; select max(age) from students; -- 查询女性的最高 身高 select max(height) from students where gender=2; -- 最小值 -- min -- 求和 -- sum -- 计算所有人的年龄总和 select sum(age) from students; -- 平均值 -- avg -- 计算平均年龄 select avg(age) from students; -- 计算平均年龄 sum(age)/count(*) select sum(age)/count(*) from students; -- 四舍五入 round(123.23 , 1) 保留1位小数 -- 计算所有人的平均年龄，保留2位小数 select round(sum(age)/count(*), 2) from students; select round(sum(age)/count(*), 3) from students; -- 计算男性的平均身高 保留2位小数 select round(avg(height), 2) from students where gender=1; -- select name, round(avg(height), 2) from students where gender=1; -- 分组 -- group by -- 按照性别分组,查询所有的性别 select name from students group by gender; select * from students group by gender; select gender from students group by gender; -- 失败select * from students group by gender; -- 计算每种性别中的人数 select gender,count(*) from students group by gender; -- 计算男性的人数 select gender,count(*) from students where gender=1 group by gender; -- group_concat(...) -- 查询同种性别中的姓名 select gender,group_concat(name) from students where gender=1 group by gender; select gender,group_concat(name, age, id) from students where gender=1 group by gender; select gender,group_concat(name, "_", age, " ", id) from students where gender=1 group by gender; -- having -- 查询平均年龄超过30岁的性别，以及姓名 having avg(age) > 30 select gender, group_concat(name),avg(age) from students group by gender having avg(age)>30; -- 查询每种性别中的人数多于2个的信息 select gender, group_concat(name) from students group by gender having count(*)>2; -- 分页 -- limit start, count -- 限制查询出来的数据个数 select * from students where gender=1 limit 2; -- 查询前5个数据 select * from students limit 0, 5; -- 查询id6-10（包含）的书序 select * from students limit 5, 5; -- 每页显示2个，第1个页面 select * from students limit 0,2; -- 每页显示2个，第2个页面 select * from students limit 2,2; -- 每页显示2个，第3个页面 select * from students limit 4,2; -- 每页显示2个，第4个页面 select * from students limit 6,2; -- -----> limit (第N页-1)*每个的个数, 每页的个数; -- 每页显示2个，显示第6页的信息, 按照年龄从小到大排序 -- 失败select * from students limit 2*(6-1),2; -- 失败select * from students limit 10,2 order by age asc; select * from students order by age asc limit 10,2; select * from students where gender=2 order by height desc limit 0,2; -- 连接查询 -- inner join ... on -- select ... from 表A inner join 表B; select * from students inner join classes; -- 查询 有能够对应班级的学生以及班级信息 select * from students inner join classes on students.cls_id=classes.id; -- 按照要求显示姓名、班级 select students.*, classes.name from students inner join classes on students.cls_id=classes.id; select students.name, classes.name from students inner join classes on students.cls_id=classes.id; -- 给数据表起名字 select s.name, c.name from students as s inner join classes as c on s.cls_id=c.id; -- 查询 有能够对应班级的学生以及班级信息，显示学生的所有信息，只显示班级名称 select s.*, c.name from students as s inner join classes as c on s.cls_id=c.id; -- 在以上的查询中，将班级姓名显示在第1列 select c.name, s.* from students as s inner join classes as c on s.cls_id=c.id; -- 查询 有能够对应班级的学生以及班级信息, 按照班级进行排序 -- select c.xxx s.xxx from student as s inner join clssses as c on .... order by ....; select c.name, s.* from students as s inner join classes as c on s.cls_id=c.id order by c.name; -- 当时同一个班级的时候，按照学生的id进行从小到大排序 select c.name, s.* from students as s inner join classes as c on s.cls_id=c.id order by c.name,s.id; -- left join -- 查询每位学生对应的班级信息 select * from students as s left join classes as c on s.cls_id=c.id; -- 查询没有对应班级信息的学生 -- select ... from xxx as s left join xxx as c on..... where ..... -- select ... from xxx as s left join xxx as c on..... having ..... select * from students as s left join classes as c on s.cls_id=c.id having c.id is null; select * from students as s left join classes as c on s.cls_id=c.id where c.id is null; -- right join on -- 将数据表名字互换位置，用left join完成 -- 自关联 -- 省级联动 url:http://demo.lanrenzhijia.com/2014/city0605/ -- 查询所有省份 select * from areas where pid is null; -- 查询出山东省有哪些市 select * from areas as province inner join areas as city on city.pid=province.aid having province.atitle="山东省"; select province.atitle, city.atitle from areas as province inner join areas as city on city.pid=province.aid having province.atitle="山东省"; -- 查询出青岛市有哪些县城 select province.atitle, city.atitle from areas as province inner join areas as city on city.pid=province.aid having province.atitle="青岛市"; select * from areas where pid=(select aid from areas where atitle="青岛市") -- 子查询 -- 标量子查询 -- 查询出高于平均身高的信息 -- 查询最高的男生信息 select * from students where height = 188; select * from students where height = (select max(height) from students); -- 列级子查询 -- 查询学生的班级号能够对应的学生信息 -- select * from students where cls_id in (select id from classes);

 

18 12 06 sql 的 基本语句 查询 条件查询 逻辑运算符 模糊查询 范围查询 排序 聚合函数 分组 分页 连接查询 自关联 子查询

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