三：MySQL系列之SQL查询

 

　　本篇主要介绍使用SQL查询数据库的操作，包括条件查询、排序、聚合函数、分组、分页、连接查询、自关联、子查询等命令操作。

　　首先我们先创建一个数据库、数据表、插入字段：

--------这部分在上篇以及介绍了-----------------

-- 创建数据库
create database blogs_test charset=utf8;


-- 使用数据库
use blogs_test;

-- 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
);

-- classes表
create table classes (
    id int unsigned auto_increment primary key not null,
    name varchar(30) not null
);

---------------插入记录----------------------

-- 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);

-- 向classes表中插入数据
insert into classes values (0, "python_01期"), (0, "python_02期");

---得到的students表结构如下：
+----+-----------+------+--------+--------+--------+-----------+
| id | name      | age  | height | gender | cls_id | is_delete |
+----+-----------+------+--------+--------+--------+-----------+
|  1 | 小明      |   18 | 180.00 | 女     |      1 |           |
|  2 | 小月月    |   18 | 180.00 | 女     |      2 |          |
|  3 | 彭于晏    |   29 | 185.00 | 男     |      1 |           |
|  4 | 刘德华    |   59 | 175.00 | 男     |      2 |          |
|  5 | 黄蓉      |   38 | 160.00 | 女     |      1 |           |
|  6 | 凤姐      |   28 | 150.00 | 保密   |      2 |          |
|  7 | 王祖贤    |   18 | 172.00 | 女     |      1 |          |
|  8 | 周杰伦    |   36 |   NULL | 男     |      1 |           |
|  9 | 程坤      |   27 | 181.00 | 男     |      2 |           |
| 10 | 刘亦菲    |   25 | 166.00 | 女     |      2 |           |
| 11 | 金星      |   33 | 162.00 | 中性   |      3 |          |
| 12 | 静香      |   12 | 180.00 | 女     |      4 |           |
| 13 | 郭靖      |   12 | 170.00 | 男     |      4 |           |
| 14 | 周杰      |   34 | 176.00 | 女     |      5 |           |
+----+-----------+------+--------+--------+--------+-----------+
14 rows in set (0.00 sec)

--得到的classes表结构如下：
+----+--------------+
| id | name         |
+----+--------------+
|  1 | python_01期  |
|  2 | python_02期  |
+----+--------------+
2 rows in set (0.00 sec)
创建数据库、数据表

-- 语法结构
select 字段,(聚合函数,表达式)
from 表名
where 条件

...............

order by 字段 desc
limit (第N页-1)*每个的个数

 

一、条件查询

    -- 消除重复行
    -- distinct 字段
    select district gender from students;


-- 条件查询
    -- 1、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 <>


    -- 2、逻辑运算符
        -- and
        -- 18到28岁之间所有学生的信息
        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岁以上或者身高查过180(包含)以上
        select * from students where age>18 and 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;


    --3、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.*";

        -- 查询已 周开始、伦结尾的姓名
        select name from students where name rlike "^周.*伦$";


    --4、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的名字
        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);


    --5、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;
条件查询

　　条件查询 -- 主要用 where +条件 进行查询；

 

二、排序

-- --------------- 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, age asc;

    -- 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动大到小排序
    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;
排序

　　排序 -- order by + 以什么排序；

 

三、聚合函数

-- 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 round(avg(height), 2) from students where gender=1;
聚合函数

　　聚合函数 -- count（求个数） 、max（最大值） 、min（最小值） 、sum（求和）、avg（求平均值）、round（取小数点后几位、四舍五入的方式）。聚合函数通常配合下面的分组进行使用。

 

四、分组

-- 分组
    -- group by
    -- 按照性别分组, 查询所有的性别
    --以下两种方式会报错：由于name和*的记录数和分组不同步
    select name from students group by gender;
    select * from students group by gender;

    -- 正确
    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;
分组

　　分组 -- group by + 以什么分组；group_concat（）--以分组查看组内某些信息；having -- 筛选某种组显示；

 

五、分页

-- 分页
    -- limit start, count

    -- 限制查询出来的数据格式
    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 age desc limit 0,2;
分页

　　分页 -- limit start count 从第几条数据开始显示，显示几个记录；

 

六、连接查询

-- 链接查询

    -- 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 又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 s.*, c.name from students as s left join classes as c on s.cls_id=c.id where c.name is null;
    select s.*, c.name from students as s left join classes as c on s.cls_id=c.id having c.name is null;

    -- right join
    -- 将数据表名字互换位置，用left join完成
连接查询

　　通常根据数据表B的某些条件显示数据表A的数据；inner/left/right  join ... on ..；

 

七、自关联

INSERT INTO `areas` VALUES ('110000', '北京市', NULL);
INSERT INTO `areas` VALUES ('110100', '北京市', '110000');
INSERT INTO `areas` VALUES ('110101', '东城区', '110100');
INSERT INTO `areas` VALUES ('110102', '西城区', '110100');
INSERT INTO `areas` VALUES ('110103', '朝阳区', '110100');
INSERT INTO `areas` VALUES ('110104', '丰台区', '110100');
INSERT INTO `areas` VALUES ('110105', '石景山区', '110100');
INSERT INTO `areas` VALUES ('110106', '海淀区', '110100');
INSERT INTO `areas` VALUES ('110107', '门头沟区', '110100');
INSERT INTO `areas` VALUES ('110108', '房山区', '110100');
INSERT INTO `areas` VALUES ('110109', '通州区', '110100');
INSERT INTO `areas` VALUES ('110110', '顺义区', '110100');
INSERT INTO `areas` VALUES ('110111', '昌平区', '110100');
INSERT INTO `areas` VALUES ('110112', '大兴区', '110100');
INSERT INTO `areas` VALUES ('110113', '怀柔区', '110100');
INSERT INTO `areas` VALUES ('110114', '平谷区', '110100');
INSERT INTO `areas` VALUES ('110115', '密云县', '110100');
INSERT INTO `areas` VALUES ('110116', '延庆县', '110100');
INSERT INTO `areas` VALUES ('120000', '天津市', NULL);
INSERT INTO `areas` VALUES ('120100', '天津市', '120000');
INSERT INTO `areas` VALUES ('120101', '和平区', '120100');
INSERT INTO `areas` VALUES ('120102', '河东区', '120100');
INSERT INTO `areas` VALUES ('120103', '河西区', '120100');
INSERT INTO `areas` VALUES ('120104', '南开区', '120100');
INSERT INTO `areas` VALUES ('120105', '河北区', '120100');
INSERT INTO `areas` VALUES ('120106', '红桥区', '120100');
INSERT INTO `areas` VALUES ('120107', '滨海新区', '120100');
INSERT INTO `areas` VALUES ('120108', '东丽区', '120100');
INSERT INTO `areas` VALUES ('120109', '西青区', '120100');
INSERT INTO `areas` VALUES ('120110', '津南区', '120100');
INSERT INTO `areas` VALUES ('120111', '北辰区', '120100');
INSERT INTO `areas` VALUES ('120112', '武清区', '120100');
INSERT INTO `areas` VALUES ('120113', '宝坻区', '120100');
INSERT INTO `areas` VALUES ('120114', '宁河县', '120100');
INSERT INTO `areas` VALUES ('120115', '静海县', '120100');
INSERT INTO `areas` VALUES ('120116', '蓟县', '120100');
INSERT INTO `areas` VALUES ('130000', '河北省', NULL);
INSERT INTO `areas` VALUES ('130100', '石家庄市', '130000');
INSERT INTO `areas` VALUES ('130102', '长安区', '130100');
INSERT INTO `areas` VALUES ('130103', '桥东区', '130100');
INSERT INTO `areas` VALUES ('130104', '桥西区', '130100');
INSERT INTO `areas` VALUES ('130105', '新华区', '130100');
INSERT INTO `areas` VALUES ('130107', '井陉矿区', '130100');
INSERT INTO `areas` VALUES ('130108', '裕华区', '130100');
INSERT INTO `areas` VALUES ('130121', '井陉县', '130100');
INSERT INTO `areas` VALUES ('130123', '正定县', '130100');
INSERT INTO `areas` VALUES ('130124', '栾城县', '130100');
INSERT INTO `areas` VALUES ('130125', '行唐县', '130100');
INSERT INTO `areas` VALUES ('130126', '灵寿县', '130100');
INSERT INTO `areas` VALUES ('130127', '高邑县', '130100');
INSERT INTO `areas` VALUES ('130128', '深泽县', '130100');
INSERT INTO `areas` VALUES ('130129', '赞皇县', '130100');
INSERT INTO `areas` VALUES ('130130', '无极县', '130100');
INSERT INTO `areas` VALUES ('130131', '平山县', '130100');
INSERT INTO `areas` VALUES ('130132', '元氏县', '130100');
INSERT INTO `areas` VALUES ('130133', '赵县', '130100');
INSERT INTO `areas` VALUES ('130181', '辛集市', '130100');
INSERT INTO `areas` VALUES ('130182', '藁城市', '130100');
INSERT INTO `areas` VALUES ('130183', '晋州市', '130100');
INSERT INTO `areas` VALUES ('130184', '新乐市', '130100');
INSERT INTO `areas` VALUES ('130185', '鹿泉市', '130100');
INSERT INTO `areas` VALUES ('130200', '唐山市', '130000');
INSERT INTO `areas` VALUES ('130202', '路南区', '130200');
INSERT INTO `areas` VALUES ('130203', '路北区', '130200');
INSERT INTO `areas` VALUES ('130204', '古冶区', '130200');
INSERT INTO `areas` VALUES ('130205', '开平区', '130200');
INSERT INTO `areas` VALUES ('130207', '丰南区', '130200');
INSERT INTO `areas` VALUES ('130208', '丰润区', '130200');
INSERT INTO `areas` VALUES ('130223', '滦县', '130200');
INSERT INTO `areas` VALUES ('130224', '滦南县', '130200');
INSERT INTO `areas` VALUES ('130225', '乐亭县', '130200');
INSERT INTO `areas` VALUES ('130227', '迁西县', '130200');
INSERT INTO `areas` VALUES ('130229', '玉田县', '130200');
INSERT INTO `areas` VALUES ('130230', '唐海县', '130200');
INSERT INTO `areas` VALUES ('130281', '遵化市', '130200');
INSERT INTO `areas` VALUES ('130283', '迁安市', '130200');
INSERT INTO `areas` VALUES ('130300', '秦皇岛市', '130000');
INSERT INTO `areas` VALUES ('130301', '海港区', '130300');
INSERT INTO `areas` VALUES ('130303', '山海关区', '130300');
INSERT INTO `areas` VALUES ('130304', '北戴河区', '130300');
INSERT INTO `areas` VALUES ('130321', '青龙满族自治县', '130300');
INSERT INTO `areas` VALUES ('130322', '昌黎县', '130300');
INSERT INTO `areas` VALUES ('130323', '抚宁县', '130300');
INSERT INTO `areas` VALUES ('130324', '卢龙县', '130300');
INSERT INTO `areas` VALUES ('130400', '邯郸市', '130000');
INSERT INTO `areas` VALUES ('130402', '邯山区', '130400');
INSERT INTO `areas` VALUES ('130403', '丛台区', '130400');
INSERT INTO `areas` VALUES ('130404', '复兴区', '130400');
INSERT INTO `areas` VALUES ('130406', '峰峰矿区', '130400');
INSERT INTO `areas` VALUES ('130421', '邯郸县', '130400');
INSERT INTO `areas` VALUES ('130423', '临漳县', '130400');
INSERT INTO `areas` VALUES ('130424', '成安县', '130400');
INSERT INTO `areas` VALUES ('130425', '大名县', '130400');
INSERT INTO `areas` VALUES ('130426', '涉县', '130400');
INSERT INTO `areas` VALUES ('130427', '磁县', '130400');
INSERT INTO `areas` VALUES ('130428', '肥乡县', '130400');
INSERT INTO `areas` VALUES ('130429', '永年县', '130400');
INSERT INTO `areas` VALUES ('130430', '邱县', '130400');
INSERT INTO `areas` VALUES ('130431', '鸡泽县', '130400');
INSERT INTO `areas` VALUES ('130432', '广平县', '130400');
INSERT INTO `areas` VALUES ('130433', '馆陶县', '130400');
INSERT INTO `areas` VALUES ('130434', '魏县', '130400');
INSERT INTO `areas` VALUES ('130435', '曲周县', '130400');
INSERT INTO `areas` VALUES ('130481', '武安市', '130400');
INSERT INTO `areas` VALUES ('130500', '邢台市', '130000');
INSERT INTO `areas` VALUES ('130502', '桥东区', '130500');
INSERT INTO `areas` VALUES ('130503', '桥西区', '130500');
INSERT INTO `areas` VALUES ('130521', '邢台县', '130500');
INSERT INTO `areas` VALUES ('130522', '临城县', '130500');
INSERT INTO `areas` VALUES ('130523', '内丘县', '130500');
INSERT INTO `areas` VALUES ('130524', '柏乡县', '130500');
INSERT INTO `areas` VALUES ('130525', '隆尧县', '130500');
INSERT INTO `areas` VALUES ('130526', '任县', '130500');
INSERT INTO `areas` VALUES ('130527', '南和县', '130500');
INSERT INTO `areas` VALUES ('130528', '宁晋县', '130500');
INSERT INTO `areas` VALUES ('130529', '巨鹿县', '130529');
INSERT INTO `areas` VALUES ('130530', '新河县', '130500');
INSERT INTO `areas` VALUES ('130531', '广宗县', '130500');
INSERT INTO `areas` VALUES ('130532', '平乡县', '130500');
INSERT INTO `areas` VALUES ('130533', '威县', '130500');
INSERT INTO `areas` VALUES ('130534', '清河县', '130500');
INSERT INTO `areas` VALUES ('130535', '临西县', '130500');
INSERT INTO `areas` VALUES ('130581', '南宫市', '130500');
INSERT INTO `areas` VALUES ('130582', '沙河市', '130500');
INSERT INTO `areas` VALUES ('130600', '保定市', '130000');
INSERT INTO `areas` VALUES ('130601', '新市区', '130600');
INSERT INTO `areas` VALUES ('130603', '北市区', '130600');
INSERT INTO `areas` VALUES ('130604', '南市区', '130600');
INSERT INTO `areas` VALUES ('130621', '满城县', '130600');
INSERT INTO `areas` VALUES ('130622', '清苑县', '130600');
INSERT INTO `areas` VALUES ('130623', '涞水县', '130600');
INSERT INTO `areas` VALUES ('130624', '阜平县', '130600');
INSERT INTO `areas` VALUES ('130625', '徐水县', '130600');
INSERT INTO `areas` VALUES ('130626', '定兴县', '130600');
INSERT INTO `areas` VALUES ('130627', '唐县', '130600');
INSERT INTO `areas` VALUES ('130628', '高阳县', '130600');
INSERT INTO `areas` VALUES ('130629', '容城县', '130600');
INSERT INTO `areas` VALUES ('130630', '涞源县', '130600');
INSERT INTO `areas` VALUES ('130631', '望都县', '130600');
INSERT INTO `areas` VALUES ('130632', '安新县', '130600');
INSERT INTO `areas` VALUES ('130633', '易县', '130600');
INSERT INTO `areas` VALUES ('130634', '曲阳县', '130600');
INSERT INTO `areas` VALUES ('130635', '蠡县', '130600');
INSERT INTO `areas` VALUES ('130636', '顺平县', '130600');
INSERT INTO `areas` VALUES ('130637', '博野县', '130600');
INSERT INTO `areas` VALUES ('130638', '雄县', '130600');
INSERT INTO `areas` VALUES ('130681', '涿州市', '130600');
INSERT INTO `areas` VALUES ('130682', '定州市', '130600');
INSERT INTO `areas` VALUES ('130683', '安国市', '130600');
INSERT INTO `areas` VALUES ('130684', '高碑店市', '130600');
INSERT INTO `areas` VALUES ('130685', '白沟新城县', '130600');
INSERT INTO `areas` VALUES ('130700', '张家口市', '130000');
INSERT INTO `areas` VALUES ('130702', '桥东区', '130700');
INSERT INTO `areas` VALUES ('130703', '桥西区', '130700');
INSERT INTO `areas` VALUES ('130705', '宣化区', '130700');
INSERT INTO `areas` VALUES ('130706', '下花园区', '130700');
INSERT INTO `areas` VALUES ('130721', '宣化县', '130700');
INSERT INTO `areas` VALUES ('130722', '张北县', '130700');
INSERT INTO `areas` VALUES ('130723', '康保县', '130700');
INSERT INTO `areas` VALUES ('130724', '沽源县', '130700');
INSERT INTO `areas` VALUES ('130725', '尚义县', '130700');
INSERT INTO `areas` VALUES ('130726', '蔚县', '130700');
INSERT INTO `areas` VALUES ('130727', '阳原县', '130700');
INSERT INTO `areas` VALUES ('130728', '怀安县', '130700');
INSERT INTO `areas` VALUES ('130729', '万全县', '130700');
INSERT INTO `areas` VALUES ('130730', '怀来县', '130700');
INSERT INTO `areas` VALUES ('130731', '涿鹿县', '130700');
INSERT INTO `areas` VALUES ('130732', '赤城县', '130700');
INSERT INTO `areas` VALUES ('130733', '崇礼县', '130700');
INSERT INTO `areas` VALUES ('130800', '承德市', '130000');
INSERT INTO `areas` VALUES ('130802', '双桥区', '130800');
INSERT INTO `areas` VALUES ('130803', '双滦区', '130800');
INSERT INTO `areas` VALUES ('130804', '鹰手营子矿区', '130800');
INSERT INTO `areas` VALUES ('130821', '承德县', '130800');
INSERT INTO `areas` VALUES ('130822', '兴隆县', '130800');
INSERT INTO `areas` VALUES ('130823', '平泉县', '130800');
INSERT INTO `areas` VALUES ('130824', '滦平县', '130800');
INSERT INTO `areas` VALUES ('130825', '隆化县', '130800');
INSERT INTO `areas` VALUES ('130826', '丰宁满族自治县', '130800');
INSERT INTO `areas` VALUES ('130827', '宽城满族自治县', '130800');
INSERT INTO `areas` VALUES ('130828', '围场满族蒙古族自治县', '130800');
INSERT INTO `areas` VALUES ('130900', '沧州市', '130000');
INSERT INTO `areas` VALUES ('130902', '新华区', '130900');
INSERT INTO `areas` VALUES ('130903', '运河区', '130900');
INSERT INTO `areas` VALUES ('130921', '沧县', '130900');
INSERT INTO `areas` VALUES ('130922', '青县', '130900');
INSERT INTO `areas` VALUES ('130923', '东光县', '130900');
INSERT INTO `areas` VALUES ('130924', '海兴县', '130900');
INSERT INTO `areas` VALUES ('130925', '盐山县', '130900');
INSERT INTO `areas` VALUES ('130926', '肃宁县', '130900');
INSERT INTO `areas` VALUES ('130927', '南皮县', '130900');
INSERT INTO `areas` VALUES ('130928', '吴桥县', '130900');
INSERT INTO `areas` VALUES ('130929', '献县', '130900');
INSERT INTO `areas` VALUES ('130930', '孟村回族自治县', '130900');
INSERT INTO `areas` VALUES ('130981', '泊头市', '130900');
INSERT INTO `areas` VALUES ('130982', '任丘市', '130900');
INSERT INTO `areas` VALUES ('130983', '黄骅市', '130900');
INSERT INTO `areas` VALUES ('130984', '河间市', '130900');
INSERT INTO `areas` VALUES ('131000', '廊坊市', '130000');
INSERT INTO `areas` VALUES ('131002', '安次区', '131000');
INSERT INTO `areas` VALUES ('131003', '广阳区', '131000');
INSERT INTO `areas` VALUES ('131022', '固安县', '131000');
INSERT INTO `areas` VALUES ('131023', '永清县', '131000');
INSERT INTO `areas` VALUES ('131024', '香河县', '131000');
INSERT INTO `areas` VALUES ('131025', '大城县', '131000');
INSERT INTO `areas` VALUES ('131026', '文安县', '131000');
INSERT INTO `areas` VALUES ('131028', '大厂回族自治县', '131000');
INSERT INTO `areas` VALUES ('131081', '霸州市', '131000');
INSERT INTO `areas` VALUES ('131082', '三河市', '131000');
INSERT INTO `areas` VALUES ('131100', '衡水市', '130000');
INSERT INTO `areas` VALUES ('131102', '桃城区', '131100');
INSERT INTO `areas` VALUES ('131121', '枣强县', '131100');
INSERT INTO `areas` VALUES ('131122', '武邑县', '131100');
INSERT INTO `areas` VALUES ('131123', '武强县', '131100');
INSERT INTO `areas` VALUES ('131124', '饶阳县', '131100');
INSERT INTO `areas` VALUES ('131125', '安平县', '131100');
INSERT INTO `areas` VALUES ('131126', '故城县', '131100');
INSERT INTO `areas` VALUES ('131127', '景县', '131100');
INSERT INTO `areas` VALUES ('131128', '阜城县', '131100');
INSERT INTO `areas` VALUES ('131181', '冀州市', '131100');
INSERT INTO `areas` VALUES ('131182', '深州市', '131100');
某几个省市县的数据

　　由于每个省、市、以及县的数据均在一个表内，这时候我们需要用到自关联,由于省的aid == 市的pid，而市的aid == 县的pid，则：

 --- 创建一个表将上面的数据插入
    create table areas(
        aid int primary key,
        atitle varchar(20),
        pid int
    ); 

 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 * from areas as city inner join areas as province on city.pid=province.aid where province.atitle="青岛市";
自查询

　　其实相当于将一个表做两次命名，再做连接查询；

 

八、子查询

-- 子查询
    -- 标量子查询
    -- 查询出高于平均身高的信息
    select * from students where height > (select avg(height) from students);

    -- 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 (1, 2);
    select * from students where cls_id in (select id from classes);
子查询

　　主要通过将子查询的结果作为值传入，用做其他地方；

 

　　over~~~ 本篇关系某培训机构的的课件~~~~，只是方便记忆~~~~

posted @ 2018-07-26 23:06  Little_five  阅读(438)  评论(0)  编辑  收藏  举报