mysql_study_2

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;