select
代码：
CREATE DATABASE mysql_shiyan;use mysql_shiyan;CREATE TABLE department
(
dpt_name CHAR(20) NOT NULL,
people_num INT(10) DEFAULT '',
CONSTRAINT dpt_pk PRIMARY KEY (dpt_name)
);CREATE TABLE employee
(
id INT(10) PRIMARY KEY,
name CHAR(20),
age INT(10),
salary INT(10) NOT NULL,
phone INT(12) NOT NULL,
in_dpt CHAR(20) NOT NULL,
UNIQUE (phone),
CONSTRAINT emp_fk FOREIGN KEY (in_dpt) REFERENCES department(dpt_name)
);CREATE TABLE project
(
proj_num INT(10) NOT NULL,
proj_name CHAR(20) NOT NULL,
start_date DATE NOT NULL,
end_date DATE DEFAULT '2015-04-01',
of_dpt CHAR(20) REFERENCES department(dpt_name),
CONSTRAINT proj_pk PRIMARY KEY (proj_num,proj_name)
);
插入的数据
#INSERT INTO department(dpt_name,people_num) VALUES('\u90e8\u95e8',\u4eba\u6570);INSERT INTO department(dpt_name,people_num) VALUES('dpt1',11);
INSERT INTO department(dpt_name,people_num) VALUES('dpt2',12);
INSERT INTO department(dpt_name,people_num) VALUES('dpt3',10);
INSERT INTO department(dpt_name,people_num) VALUES('dpt4',15);#INSERT INTO employee(id,name,age,salary,phone,in_dpt) VALUES(\u7f16\u53f7,'\u540d\u5b57',\u5e74\u9f84,\u5de5\u8d44,\u7535\u8bdd,'\u90e8\u95e8');INSERT INTO employee(id,name,age,salary,phone,in_dpt) VALUES(01,'Tom',26,2500,119119,'dpt4');
INSERT INTO employee(id,name,age,salary,phone,in_dpt) VALUES(02,'Jack',24,2500,120120,'dpt2');
INSERT INTO employee(id,name,age,salary,phone,in_dpt) VALUES(03,'Rose',22,2800,114114,'dpt3');
INSERT INTO employee(id,name,age,salary,phone,in_dpt) VALUES(04,'Jim',35,3000,100861,'dpt1');
INSERT INTO employee(id,name,age,salary,phone,in_dpt) VALUES(05,'Mary',21,3000,100101,'dpt2');
INSERT INTO employee(id,name,age,salary,phone,in_dpt) VALUES(06,'Alex',26,3000,123456,'dpt1');
INSERT INTO employee(id,name,age,salary,phone,in_dpt) VALUES(07,'Ken',27,3500,654321,'dpt1');
INSERT INTO employee(id,name,age,salary,phone,in_dpt) VALUES(08,'Rick',24,3500,987654,'dpt3');
INSERT INTO employee(id,name,age,salary,phone,in_dpt) VALUES(09,'Joe',31,3600,110129,'dpt2');
INSERT INTO employee(id,name,age,salary,phone,in_dpt) VALUES(10,'Mike',23,3400,110110,'dpt4');
INSERT INTO employee(id,name,salary,phone,in_dpt) VALUES(11,'Jobs',3600,019283,'dpt2');
INSERT INTO employee(id,name,salary,phone,in_dpt) VALUES(12,'Tony',3400,102938,'dpt3');#INSERT INTO project(proj_num,proj_name,start_date,end_date,of_dpt) VALUES(\u7f16\u53f7,'\u5de5\u7a0b\u540d','\u5f00\u59cb\u65f6\u95f4','\u7ed3\u675f\u65f6\u95f4','\u90e8\u95e8\u540d');INSERT INTO project(proj_num,proj_name,start_date,end_date,of_dpt) VALUES(01,'proj_a','2015-01-15','2015-01-31','dpt2');
INSERT INTO project(proj_num,proj_name,start_date,end_date,of_dpt) VALUES(02,'proj_b','2015-01-15','2015-02-15','dpt1');
INSERT INTO project(proj_num,proj_name,start_date,end_date,of_dpt) VALUES(03,'proj_c','2015-02-01','2015-03-01','dpt4');
INSERT INTO project(proj_num,proj_name,start_date,end_date,of_dpt) VALUES(04,'proj_d','2015-02-15','2015-04-01','dpt3');
INSERT INTO project(proj_num,proj_name,start_date,end_date,of_dpt) VALUES(05,'proj_e','2015-02-25','2015-03-01','dpt4');
INSERT INTO project(proj_num,proj_name,start_date,end_date,of_dpt) VALUES(06,'proj_f','2015-02-26','2015-03-01','dpt2');
SELECT 要查询的列名 FROM 表名字 WHERE 限制条件;
简单限制条件
1……..and || or || between and …..and
2…….. in || not in
关键词 IN 和 NOT IN 的作用和它们的名字一样明显，用于筛选“在”或“不在”某个范围内的结果，比如说我们要查询在 dpt3 或 dpt4 的人:
SELECT name,age,phone,in_dpt FROM employee WHERE in_dpt IN ('dpt3','dpt4');
而 NOT IN 的效果则是，如下面这条命令，查询出了不在 dpt1 也不在 dpt3 的人：
SELECT name,age,phone,in_dpt FROM employee WHERE in_dpt NOT IN ('dpt1','dpt3');
通配符
关键字 LIKE 可用于实现模糊查询，常见于搜索功能中。
和 LIKE 联用的通常还有通配符，代表未知字符。 SQL中的通配符是 _ 和 % 。其中 _ 代表一个未指定字符，% 代表不定个未指定字符
排序：
order by XXX desc 降序|| asc 升序 不过 也可以不加表示 升序
内置函数和计算
其中 COUNT 函数可用于任何数据类型(因为它只是计数)，而 SUM 、AVG 函数都只能对数字类数据类型做计算，MAX 和 MIN 可用于数值、字符串或是日期时间数据类型。
SELECT MAX(salary) AS max_salary,MIN(salary) FROM employee;
有一个细节你或许注意到了，使用 AS 关键词可以给值重命名，比如最大值被命名为了 max_salary：
子查询
想要知道名为 “Tom” 的员工所在部门做了几个工程。员工信息储存在 employee 表中，但工程信息储存在 project 表中。
对于这样的情况，我们可以用子查询：
SELECT of_dpt,COUNT(proj_name) AS count_project FROM project GROUP BY of_dpt
HAVING of_dpt IN
(SELECT in_dpt FROM employee WHERE name='Tom');
上面代码包含两个 SELECT 语句，第二个 SELECT 语句将返回一个集合的数据形式，然后被第一个 SELECT 语句用 in 进行判断。
HAVING 关键字可以的作用和 WHERE 是一样的，都是说明接下来要进行条件筛选操作。
区别在于 HAVING 用于对分组后的数据进行筛选
group by …..having……
连接查询
SELECT id,name,people_num
FROM employee,department
WHERE employee.in_dpt = department.dpt_name
ORDER BY id;
等同于
SELECT id,name,people_num
FROM employee JOIN department
ON employee.in_dpt = department.dpt_name
ORDER BY id;
