-- 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 ); -- classes表 CREATE TABLE classes ( id INT UNSIGNED AUTO_INCREMENT PRIMARY KEY NOT NULL, NAME VARCHAR(30) NOT NULL ); -- 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);