一文让你搞懂Mysql中 concat函数，ifnull函数，distinct，+号的使用

数据库的好处：

1：持久化数据到本地
2：可以实现结构化查询，方便管理

数据库相关概念：

1：DB，数据库，保存一组有组织的数据的容器。

2：DBMS，数据库管理系统，又称为数据库软件(产品)，用于管理DB中的数据

3：SQL,结构化查询语言，用于和数据库通信的语言，不是某个数据库团建特有的，而实几乎所有的主流数据库软件通用的语言。

数据库存储数据的特点

1：数据存放到表中，然后表再放到库中。

2：一个库中可以有多张表，每张表具有唯一的表明来表示自己

3：表中有一个或多个列，列又称为字段，相当于java中的属性

4：表中每一行数据，相当于java中的对象。

Mysql服务的登录和退出

登录：mysql [-h主机名 -p端口号] -u用户名 -p密码

退出:exit 或 ctrl+c

Mysql 的常见命令

1.查看当前所以的数据库  show databases;

2.打开指定库的指令：use 库名;

3.查看当前库的所有表 show tables;

4.查看其他库的所有表 show tables from 库名

5.查看表结构  desc 表名;

6.查看服务器的版本    

	方式一：登录到mysql服务器端  select version();

	方式二:没有登录到mysql服务器端  mysql  ---version  或 mysql --V

Mysql的语法规范

1.不区分大小写，但建议关键字大写，表名，列表小写

2.每条命令最好使用分号结尾

3.每条命令根据需要，可以进行缩进或换行。

4.注释  

	单行注释：# 注释文字

	单行注释: --  注释文字

	多行注释: /*  注释文字*/

Mysql练习所用到的数据库即表数据

大家可以观看这个视频下面就是需要使用的sql语句 https://www.bilibili.com/video/BV12b411K7Zu?p=37

首先创建数据库:

create database myemployees;

导入数据

/*
 Navicat Premium Data Transfer

 Source Server         : mysql主库
 Source Server Type    : MySQL
 Source Server Version : 50727
 Source Host           : localhost:3306
 Source Schema         : myemployees

 Target Server Type    : MySQL
 Target Server Version : 50727
 File Encoding         : 65001

 Date: 08/05/2020 15:52:52
*/

SET NAMES utf8mb4;
SET FOREIGN_KEY_CHECKS = 0;

-- ----------------------------
-- Table structure for departments
-- ----------------------------
DROP TABLE IF EXISTS `departments`;
CREATE TABLE `departments`  (
  `department_id` int(4) NOT NULL AUTO_INCREMENT,
  `department_name` varchar(3) CHARACTER SET gb2312 COLLATE gb2312_chinese_ci NULL DEFAULT NULL,
  `manager_id` int(6) NULL DEFAULT NULL,
  `location_id` int(4) NULL DEFAULT NULL,
  PRIMARY KEY (`department_id`) USING BTREE,
  INDEX `loc_id_fk`(`location_id`) USING BTREE,
  CONSTRAINT `loc_id_fk` FOREIGN KEY (`location_id`) REFERENCES `locations` (`location_id`) ON DELETE RESTRICT ON UPDATE RESTRICT
) ENGINE = InnoDB AUTO_INCREMENT = 271 CHARACTER SET = gb2312 COLLATE = gb2312_chinese_ci ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of departments
-- ----------------------------
INSERT INTO `departments` VALUES (10, 'Adm', 200, 1700);
INSERT INTO `departments` VALUES (20, 'Mar', 201, 1800);
INSERT INTO `departments` VALUES (30, 'Pur', 114, 1700);
INSERT INTO `departments` VALUES (40, 'Hum', 203, 2400);
INSERT INTO `departments` VALUES (50, 'Shi', 121, 1500);
INSERT INTO `departments` VALUES (60, 'IT', 103, 1400);
INSERT INTO `departments` VALUES (70, 'Pub', 204, 2700);
INSERT INTO `departments` VALUES (80, 'Sal', 145, 2500);
INSERT INTO `departments` VALUES (90, 'Exe', 100, 1700);
INSERT INTO `departments` VALUES (100, 'Fin', 108, 1700);
INSERT INTO `departments` VALUES (110, 'Acc', 205, 1700);
INSERT INTO `departments` VALUES (120, 'Tre', NULL, 1700);
INSERT INTO `departments` VALUES (130, 'Cor', NULL, 1700);
INSERT INTO `departments` VALUES (140, 'Con', NULL, 1700);
INSERT INTO `departments` VALUES (150, 'Sha', NULL, 1700);
INSERT INTO `departments` VALUES (160, 'Ben', NULL, 1700);
INSERT INTO `departments` VALUES (170, 'Man', NULL, 1700);
INSERT INTO `departments` VALUES (180, 'Con', NULL, 1700);
INSERT INTO `departments` VALUES (190, 'Con', NULL, 1700);
INSERT INTO `departments` VALUES (200, 'Ope', NULL, 1700);
INSERT INTO `departments` VALUES (210, 'IT ', NULL, 1700);
INSERT INTO `departments` VALUES (220, 'NOC', NULL, 1700);
INSERT INTO `departments` VALUES (230, 'IT ', NULL, 1700);
INSERT INTO `departments` VALUES (240, 'Gov', NULL, 1700);
INSERT INTO `departments` VALUES (250, 'Ret', NULL, 1700);
INSERT INTO `departments` VALUES (260, 'Rec', NULL, 1700);
INSERT INTO `departments` VALUES (270, 'Pay', NULL, 1700);

-- ----------------------------
-- Table structure for employees
-- ----------------------------
DROP TABLE IF EXISTS `employees`;
CREATE TABLE `employees`  (
  `employee_id` int(6) NOT NULL AUTO_INCREMENT,
  `first_name` varchar(20) CHARACTER SET gb2312 COLLATE gb2312_chinese_ci NULL DEFAULT NULL,
  `last_name` varchar(25) CHARACTER SET gb2312 COLLATE gb2312_chinese_ci NULL DEFAULT NULL,
  `email` varchar(25) CHARACTER SET gb2312 COLLATE gb2312_chinese_ci NULL DEFAULT NULL,
  `phone_number` varchar(20) CHARACTER SET gb2312 COLLATE gb2312_chinese_ci NULL DEFAULT NULL,
  `job_id` varchar(10) CHARACTER SET gb2312 COLLATE gb2312_chinese_ci NULL DEFAULT NULL,
  `salary` double(10, 2) NULL DEFAULT NULL,
  `commission_pct` double(4, 2) NULL DEFAULT NULL,
  `manager_id` int(6) NULL DEFAULT NULL,
  `department_id` int(4) NULL DEFAULT NULL,
  `hiredate` datetime(0) NULL DEFAULT NULL,
  PRIMARY KEY (`employee_id`) USING BTREE,
  INDEX `dept_id_fk`(`department_id`) USING BTREE,
  INDEX `job_id_fk`(`job_id`) USING BTREE,
  CONSTRAINT `dept_id_fk` FOREIGN KEY (`department_id`) REFERENCES `departments` (`department_id`) ON DELETE RESTRICT ON UPDATE RESTRICT,
  CONSTRAINT `job_id_fk` FOREIGN KEY (`job_id`) REFERENCES `jobs` (`job_id`) ON DELETE RESTRICT ON UPDATE RESTRICT
) ENGINE = InnoDB AUTO_INCREMENT = 207 CHARACTER SET = gb2312 COLLATE = gb2312_chinese_ci ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of employees
-- ----------------------------
INSERT INTO `employees` VALUES (100, 'Steven', 'K_ing', 'SKING', '515.123.4567', 'AD_PRES', 24000.00, NULL, NULL, 90, '1992-04-03 00:00:00');
INSERT INTO `employees` VALUES (101, 'Neena', 'Kochhar', 'NKOCHHAR', '515.123.4568', 'AD_VP', 17000.00, NULL, 100, 90, '1992-04-03 00:00:00');
INSERT INTO `employees` VALUES (102, 'Lex', 'De Haan', 'LDEHAAN', '515.123.4569', 'AD_VP', 17000.00, NULL, 100, 90, '1992-04-03 00:00:00');
INSERT INTO `employees` VALUES (103, 'Alexander', 'Hunold', 'AHUNOLD', '590.423.4567', 'IT_PROG', 9000.00, NULL, 102, 60, '1992-04-03 00:00:00');
INSERT INTO `employees` VALUES (104, 'Bruce', 'Ernst', 'BERNST', '590.423.4568', 'IT_PROG', 6000.00, NULL, 103, 60, '1992-04-03 00:00:00');
INSERT INTO `employees` VALUES (105, 'David', 'Austin', 'DAUSTIN', '590.423.4569', 'IT_PROG', 4800.00, NULL, 103, 60, '1998-03-03 00:00:00');
INSERT INTO `employees` VALUES (106, 'Valli', 'Pataballa', 'VPATABAL', '590.423.4560', 'IT_PROG', 4800.00, NULL, 103, 60, '1998-03-03 00:00:00');
INSERT INTO `employees` VALUES (107, 'Diana', 'Lorentz', 'DLORENTZ', '590.423.5567', 'IT_PROG', 4200.00, NULL, 103, 60, '1998-03-03 00:00:00');
INSERT INTO `employees` VALUES (108, 'Nancy', 'Greenberg', 'NGREENBE', '515.124.4569', 'FI_MGR', 12000.00, NULL, 101, 100, '1998-03-03 00:00:00');
INSERT INTO `employees` VALUES (109, 'Daniel', 'Faviet', 'DFAVIET', '515.124.4169', 'FI_ACCOUNT', 9000.00, NULL, 108, 100, '1998-03-03 00:00:00');
INSERT INTO `employees` VALUES (110, 'John', 'Chen', 'JCHEN', '515.124.4269', 'FI_ACCOUNT', 8200.00, NULL, 108, 100, '2000-09-09 00:00:00');
INSERT INTO `employees` VALUES (111, 'Ismael', 'Sciarra', 'ISCIARRA', '515.124.4369', 'FI_ACCOUNT', 7700.00, NULL, 108, 100, '2000-09-09 00:00:00');
INSERT INTO `employees` VALUES (112, 'Jose Manuel', 'Urman', 'JMURMAN', '515.124.4469', 'FI_ACCOUNT', 7800.00, NULL, 108, 100, '2000-09-09 00:00:00');
INSERT INTO `employees` VALUES (113, 'Luis', 'Popp', 'LPOPP', '515.124.4567', 'FI_ACCOUNT', 6900.00, NULL, 108, 100, '2000-09-09 00:00:00');
INSERT INTO `employees` VALUES (114, 'Den', 'Raphaely', 'DRAPHEAL', '515.127.4561', 'PU_MAN', 11000.00, NULL, 100, 30, '2000-09-09 00:00:00');
INSERT INTO `employees` VALUES (115, 'Alexander', 'Khoo', 'AKHOO', '515.127.4562', 'PU_CLERK', 3100.00, NULL, 114, 30, '2000-09-09 00:00:00');
INSERT INTO `employees` VALUES (116, 'Shelli', 'Baida', 'SBAIDA', '515.127.4563', 'PU_CLERK', 2900.00, NULL, 114, 30, '2000-09-09 00:00:00');
INSERT INTO `employees` VALUES (117, 'Sigal', 'Tobias', 'STOBIAS', '515.127.4564', 'PU_CLERK', 2800.00, NULL, 114, 30, '2000-09-09 00:00:00');
INSERT INTO `employees` VALUES (118, 'Guy', 'Himuro', 'GHIMURO', '515.127.4565', 'PU_CLERK', 2600.00, NULL, 114, 30, '2000-09-09 00:00:00');
INSERT INTO `employees` VALUES (119, 'Karen', 'Colmenares', 'KCOLMENA', '515.127.4566', 'PU_CLERK', 2500.00, NULL, 114, 30, '2000-09-09 00:00:00');
INSERT INTO `employees` VALUES (120, 'Matthew', 'Weiss', 'MWEISS', '650.123.1234', 'ST_MAN', 8000.00, NULL, 100, 50, '2004-02-06 00:00:00');
INSERT INTO `employees` VALUES (121, 'Adam', 'Fripp', 'AFRIPP', '650.123.2234', 'ST_MAN', 8200.00, NULL, 100, 50, '2004-02-06 00:00:00');
INSERT INTO `employees` VALUES (122, 'Payam', 'Kaufling', 'PKAUFLIN', '650.123.3234', 'ST_MAN', 7900.00, NULL, 100, 50, '2004-02-06 00:00:00');
INSERT INTO `employees` VALUES (123, 'Shanta', 'Vollman', 'SVOLLMAN', '650.123.4234', 'ST_MAN', 6500.00, NULL, 100, 50, '2004-02-06 00:00:00');
INSERT INTO `employees` VALUES (124, 'Kevin', 'Mourgos', 'KMOURGOS', '650.123.5234', 'ST_MAN', 5800.00, NULL, 100, 50, '2004-02-06 00:00:00');
INSERT INTO `employees` VALUES (125, 'Julia', 'Nayer', 'JNAYER', '650.124.1214', 'ST_CLERK', 3200.00, NULL, 120, 50, '2004-02-06 00:00:00');
INSERT INTO `employees` VALUES (126, 'Irene', 'Mikkilineni', 'IMIKKILI', '650.124.1224', 'ST_CLERK', 2700.00, NULL, 120, 50, '2004-02-06 00:00:00');
INSERT INTO `employees` VALUES (127, 'James', 'Landry', 'JLANDRY', '650.124.1334', 'ST_CLERK', 2400.00, NULL, 120, 50, '2004-02-06 00:00:00');
INSERT INTO `employees` VALUES (128, 'Steven', 'Markle', 'SMARKLE', '650.124.1434', 'ST_CLERK', 2200.00, NULL, 120, 50, '2004-02-06 00:00:00');
INSERT INTO `employees` VALUES (129, 'Laura', 'Bissot', 'LBISSOT', '650.124.5234', 'ST_CLERK', 3300.00, NULL, 121, 50, '2004-02-06 00:00:00');
INSERT INTO `employees` VALUES (130, 'Mozhe', 'Atkinson', 'MATKINSO', '650.124.6234', 'ST_CLERK', 2800.00, NULL, 121, 50, '2004-02-06 00:00:00');
INSERT INTO `employees` VALUES (131, 'James', 'Marlow', 'JAMRLOW', '650.124.7234', 'ST_CLERK', 2500.00, NULL, 121, 50, '2004-02-06 00:00:00');
INSERT INTO `employees` VALUES (132, 'TJ', 'Olson', 'TJOLSON', '650.124.8234', 'ST_CLERK', 2100.00, NULL, 121, 50, '2004-02-06 00:00:00');
INSERT INTO `employees` VALUES (133, 'Jason', 'Mallin', 'JMALLIN', '650.127.1934', 'ST_CLERK', 3300.00, NULL, 122, 50, '2004-02-06 00:00:00');
INSERT INTO `employees` VALUES (134, 'Michael', 'Rogers', 'MROGERS', '650.127.1834', 'ST_CLERK', 2900.00, NULL, 122, 50, '2002-12-23 00:00:00');
INSERT INTO `employees` VALUES (135, 'Ki', 'Gee', 'KGEE', '650.127.1734', 'ST_CLERK', 2400.00, NULL, 122, 50, '2002-12-23 00:00:00');
INSERT INTO `employees` VALUES (136, 'Hazel', 'Philtanker', 'HPHILTAN', '650.127.1634', 'ST_CLERK', 2200.00, NULL, 122, 50, '2002-12-23 00:00:00');
INSERT INTO `employees` VALUES (137, 'Renske', 'Ladwig', 'RLADWIG', '650.121.1234', 'ST_CLERK', 3600.00, NULL, 123, 50, '2002-12-23 00:00:00');
INSERT INTO `employees` VALUES (138, 'Stephen', 'Stiles', 'SSTILES', '650.121.2034', 'ST_CLERK', 3200.00, NULL, 123, 50, '2002-12-23 00:00:00');
INSERT INTO `employees` VALUES (139, 'John', 'Seo', 'JSEO', '650.121.2019', 'ST_CLERK', 2700.00, NULL, 123, 50, '2002-12-23 00:00:00');
INSERT INTO `employees` VALUES (140, 'Joshua', 'Patel', 'JPATEL', '650.121.1834', 'ST_CLERK', 2500.00, NULL, 123, 50, '2002-12-23 00:00:00');
INSERT INTO `employees` VALUES (141, 'Trenna', 'Rajs', 'TRAJS', '650.121.8009', 'ST_CLERK', 3500.00, NULL, 124, 50, '2002-12-23 00:00:00');
INSERT INTO `employees` VALUES (142, 'Curtis', 'Davies', 'CDAVIES', '650.121.2994', 'ST_CLERK', 3100.00, NULL, 124, 50, '2002-12-23 00:00:00');
INSERT INTO `employees` VALUES (143, 'Randall', 'Matos', 'RMATOS', '650.121.2874', 'ST_CLERK', 2600.00, NULL, 124, 50, '2002-12-23 00:00:00');
INSERT INTO `employees` VALUES (144, 'Peter', 'Vargas', 'PVARGAS', '650.121.2004', 'ST_CLERK', 2500.00, NULL, 124, 50, '2002-12-23 00:00:00');
INSERT INTO `employees` VALUES (145, 'John', 'Russell', 'JRUSSEL', '011.44.1344.429268', 'SA_MAN', 14000.00, 0.40, 100, 80, '2002-12-23 00:00:00');
INSERT INTO `employees` VALUES (146, 'Karen', 'Partners', 'KPARTNER', '011.44.1344.467268', 'SA_MAN', 13500.00, 0.30, 100, 80, '2002-12-23 00:00:00');
INSERT INTO `employees` VALUES (147, 'Alberto', 'Errazuriz', 'AERRAZUR', '011.44.1344.429278', 'SA_MAN', 12000.00, 0.30, 100, 80, '2002-12-23 00:00:00');
INSERT INTO `employees` VALUES (148, 'Gerald', 'Cambrault', 'GCAMBRAU', '011.44.1344.619268', 'SA_MAN', 11000.00, 0.30, 100, 80, '2002-12-23 00:00:00');
INSERT INTO `employees` VALUES (149, 'Eleni', 'Zlotkey', 'EZLOTKEY', '011.44.1344.429018', 'SA_MAN', 10500.00, 0.20, 100, 80, '2002-12-23 00:00:00');
INSERT INTO `employees` VALUES (150, 'Peter', 'Tucker', 'PTUCKER', '011.44.1344.129268', 'SA_REP', 10000.00, 0.30, 145, 80, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (151, 'David', 'Bernstein', 'DBERNSTE', '011.44.1344.345268', 'SA_REP', 9500.00, 0.25, 145, 80, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (152, 'Peter', 'Hall', 'PHALL', '011.44.1344.478968', 'SA_REP', 9000.00, 0.25, 145, 80, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (153, 'Christopher', 'Olsen', 'COLSEN', '011.44.1344.498718', 'SA_REP', 8000.00, 0.20, 145, 80, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (154, 'Nanette', 'Cambrault', 'NCAMBRAU', '011.44.1344.987668', 'SA_REP', 7500.00, 0.20, 145, 80, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (155, 'Oliver', 'Tuvault', 'OTUVAULT', '011.44.1344.486508', 'SA_REP', 7000.00, 0.15, 145, 80, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (156, 'Janette', 'K_ing', 'JKING', '011.44.1345.429268', 'SA_REP', 10000.00, 0.35, 146, 80, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (157, 'Patrick', 'Sully', 'PSULLY', '011.44.1345.929268', 'SA_REP', 9500.00, 0.35, 146, 80, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (158, 'Allan', 'McEwen', 'AMCEWEN', '011.44.1345.829268', 'SA_REP', 9000.00, 0.35, 146, 80, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (159, 'Lindsey', 'Smith', 'LSMITH', '011.44.1345.729268', 'SA_REP', 8000.00, 0.30, 146, 80, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (160, 'Louise', 'Doran', 'LDORAN', '011.44.1345.629268', 'SA_REP', 7500.00, 0.30, 146, 80, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (161, 'Sarath', 'Sewall', 'SSEWALL', '011.44.1345.529268', 'SA_REP', 7000.00, 0.25, 146, 80, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (162, 'Clara', 'Vishney', 'CVISHNEY', '011.44.1346.129268', 'SA_REP', 10500.00, 0.25, 147, 80, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (163, 'Danielle', 'Greene', 'DGREENE', '011.44.1346.229268', 'SA_REP', 9500.00, 0.15, 147, 80, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (164, 'Mattea', 'Marvins', 'MMARVINS', '011.44.1346.329268', 'SA_REP', 7200.00, 0.10, 147, 80, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (165, 'David', 'Lee', 'DLEE', '011.44.1346.529268', 'SA_REP', 6800.00, 0.10, 147, 80, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (166, 'Sundar', 'Ande', 'SANDE', '011.44.1346.629268', 'SA_REP', 6400.00, 0.10, 147, 80, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (167, 'Amit', 'Banda', 'ABANDA', '011.44.1346.729268', 'SA_REP', 6200.00, 0.10, 147, 80, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (168, 'Lisa', 'Ozer', 'LOZER', '011.44.1343.929268', 'SA_REP', 11500.00, 0.25, 148, 80, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (169, 'Harrison', 'Bloom', 'HBLOOM', '011.44.1343.829268', 'SA_REP', 10000.00, 0.20, 148, 80, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (170, 'Tayler', 'Fox', 'TFOX', '011.44.1343.729268', 'SA_REP', 9600.00, 0.20, 148, 80, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (171, 'William', 'Smith', 'WSMITH', '011.44.1343.629268', 'SA_REP', 7400.00, 0.15, 148, 80, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (172, 'Elizabeth', 'Bates', 'EBATES', '011.44.1343.529268', 'SA_REP', 7300.00, 0.15, 148, 80, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (173, 'Sundita', 'Kumar', 'SKUMAR', '011.44.1343.329268', 'SA_REP', 6100.00, 0.10, 148, 80, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (174, 'Ellen', 'Abel', 'EABEL', '011.44.1644.429267', 'SA_REP', 11000.00, 0.30, 149, 80, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (175, 'Alyssa', 'Hutton', 'AHUTTON', '011.44.1644.429266', 'SA_REP', 8800.00, 0.25, 149, 80, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (176, 'Jonathon', 'Taylor', 'JTAYLOR', '011.44.1644.429265', 'SA_REP', 8600.00, 0.20, 149, 80, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (177, 'Jack', 'Livingston', 'JLIVINGS', '011.44.1644.429264', 'SA_REP', 8400.00, 0.20, 149, 80, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (178, 'Kimberely', 'Grant', 'KGRANT', '011.44.1644.429263', 'SA_REP', 7000.00, 0.15, 149, NULL, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (179, 'Charles', 'Johnson', 'CJOHNSON', '011.44.1644.429262', 'SA_REP', 6200.00, 0.10, 149, 80, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (180, 'Winston', 'Taylor', 'WTAYLOR', '650.507.9876', 'SH_CLERK', 3200.00, NULL, 120, 50, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (181, 'Jean', 'Fleaur', 'JFLEAUR', '650.507.9877', 'SH_CLERK', 3100.00, NULL, 120, 50, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (182, 'Martha', 'Sullivan', 'MSULLIVA', '650.507.9878', 'SH_CLERK', 2500.00, NULL, 120, 50, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (183, 'Girard', 'Geoni', 'GGEONI', '650.507.9879', 'SH_CLERK', 2800.00, NULL, 120, 50, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (184, 'Nandita', 'Sarchand', 'NSARCHAN', '650.509.1876', 'SH_CLERK', 4200.00, NULL, 121, 50, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (185, 'Alexis', 'Bull', 'ABULL', '650.509.2876', 'SH_CLERK', 4100.00, NULL, 121, 50, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (186, 'Julia', 'Dellinger', 'JDELLING', '650.509.3876', 'SH_CLERK', 3400.00, NULL, 121, 50, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (187, 'Anthony', 'Cabrio', 'ACABRIO', '650.509.4876', 'SH_CLERK', 3000.00, NULL, 121, 50, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (188, 'Kelly', 'Chung', 'KCHUNG', '650.505.1876', 'SH_CLERK', 3800.00, NULL, 122, 50, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (189, 'Jennifer', 'Dilly', 'JDILLY', '650.505.2876', 'SH_CLERK', 3600.00, NULL, 122, 50, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (190, 'Timothy', 'Gates', 'TGATES', '650.505.3876', 'SH_CLERK', 2900.00, NULL, 122, 50, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (191, 'Randall', 'Perkins', 'RPERKINS', '650.505.4876', 'SH_CLERK', 2500.00, NULL, 122, 50, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (192, 'Sarah', 'Bell', 'SBELL', '650.501.1876', 'SH_CLERK', 4000.00, NULL, 123, 50, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (193, 'Britney', 'Everett', 'BEVERETT', '650.501.2876', 'SH_CLERK', 3900.00, NULL, 123, 50, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (194, 'Samuel', 'McCain', 'SMCCAIN', '650.501.3876', 'SH_CLERK', 3200.00, NULL, 123, 50, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (195, 'Vance', 'Jones', 'VJONES', '650.501.4876', 'SH_CLERK', 2800.00, NULL, 123, 50, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (196, 'Alana', 'Walsh', 'AWALSH', '650.507.9811', 'SH_CLERK', 3100.00, NULL, 124, 50, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (197, 'Kevin', 'Feeney', 'KFEENEY', '650.507.9822', 'SH_CLERK', 3000.00, NULL, 124, 50, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (198, 'Donald', 'OConnell', 'DOCONNEL', '650.507.9833', 'SH_CLERK', 2600.00, NULL, 124, 50, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (199, 'Douglas', 'Grant', 'DGRANT', '650.507.9844', 'SH_CLERK', 2600.00, NULL, 124, 50, '2014-03-05 00:00:00');
INSERT INTO `employees` VALUES (200, 'Jennifer', 'Whalen', 'JWHALEN', '515.123.4444', 'AD_ASST', 4400.00, NULL, 101, 10, '2016-03-03 00:00:00');
INSERT INTO `employees` VALUES (201, 'Michael', 'Hartstein', 'MHARTSTE', '515.123.5555', 'MK_MAN', 13000.00, NULL, 100, 20, '2016-03-03 00:00:00');
INSERT INTO `employees` VALUES (202, 'Pat', 'Fay', 'PFAY', '603.123.6666', 'MK_REP', 6000.00, NULL, 201, 20, '2016-03-03 00:00:00');
INSERT INTO `employees` VALUES (203, 'Susan', 'Mavris', 'SMAVRIS', '515.123.7777', 'HR_REP', 6500.00, NULL, 101, 40, '2016-03-03 00:00:00');
INSERT INTO `employees` VALUES (204, 'Hermann', 'Baer', 'HBAER', '515.123.8888', 'PR_REP', 10000.00, NULL, 101, 70, '2016-03-03 00:00:00');
INSERT INTO `employees` VALUES (205, 'Shelley', 'Higgins', 'SHIGGINS', '515.123.8080', 'AC_MGR', 12000.00, NULL, 101, 110, '2016-03-03 00:00:00');
INSERT INTO `employees` VALUES (206, 'William', 'Gietz', 'WGIETZ', '515.123.8181', 'AC_ACCOUNT', 8300.00, NULL, 205, 110, '2016-03-03 00:00:00');

-- ----------------------------
-- Table structure for jobs
-- ----------------------------
DROP TABLE IF EXISTS `jobs`;
CREATE TABLE `jobs`  (
  `job_id` varchar(10) CHARACTER SET gb2312 COLLATE gb2312_chinese_ci NOT NULL,
  `job_title` varchar(35) CHARACTER SET gb2312 COLLATE gb2312_chinese_ci NULL DEFAULT NULL,
  `min_salary` int(6) NULL DEFAULT NULL,
  `max_salary` int(6) NULL DEFAULT NULL,
  PRIMARY KEY (`job_id`) USING BTREE
) ENGINE = InnoDB CHARACTER SET = gb2312 COLLATE = gb2312_chinese_ci ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of jobs
-- ----------------------------
INSERT INTO `jobs` VALUES ('AC_ACCOUNT', 'Public Accountant', 4200, 9000);
INSERT INTO `jobs` VALUES ('AC_MGR', 'Accounting Manager', 8200, 16000);
INSERT INTO `jobs` VALUES ('AD_ASST', 'Administration Assistant', 3000, 6000);
INSERT INTO `jobs` VALUES ('AD_PRES', 'President', 20000, 40000);
INSERT INTO `jobs` VALUES ('AD_VP', 'Administration Vice President', 15000, 30000);
INSERT INTO `jobs` VALUES ('FI_ACCOUNT', 'Accountant', 4200, 9000);
INSERT INTO `jobs` VALUES ('FI_MGR', 'Finance Manager', 8200, 16000);
INSERT INTO `jobs` VALUES ('HR_REP', 'Human Resources Representative', 4000, 9000);
INSERT INTO `jobs` VALUES ('IT_PROG', 'Programmer', 4000, 10000);
INSERT INTO `jobs` VALUES ('MK_MAN', 'Marketing Manager', 9000, 15000);
INSERT INTO `jobs` VALUES ('MK_REP', 'Marketing Representative', 4000, 9000);
INSERT INTO `jobs` VALUES ('PR_REP', 'Public Relations Representative', 4500, 10500);
INSERT INTO `jobs` VALUES ('PU_CLERK', 'Purchasing Clerk', 2500, 5500);
INSERT INTO `jobs` VALUES ('PU_MAN', 'Purchasing Manager', 8000, 15000);
INSERT INTO `jobs` VALUES ('SA_MAN', 'Sales Manager', 10000, 20000);
INSERT INTO `jobs` VALUES ('SA_REP', 'Sales Representative', 6000, 12000);
INSERT INTO `jobs` VALUES ('SH_CLERK', 'Shipping Clerk', 2500, 5500);
INSERT INTO `jobs` VALUES ('ST_CLERK', 'Stock Clerk', 2000, 5000);
INSERT INTO `jobs` VALUES ('ST_MAN', 'Stock Manager', 5500, 8500);

-- ----------------------------
-- Table structure for locations
-- ----------------------------
DROP TABLE IF EXISTS `locations`;
CREATE TABLE `locations`  (
  `location_id` int(11) NOT NULL AUTO_INCREMENT,
  `street_address` varchar(40) CHARACTER SET gb2312 COLLATE gb2312_chinese_ci NULL DEFAULT NULL,
  `postal_code` varchar(12) CHARACTER SET gb2312 COLLATE gb2312_chinese_ci NULL DEFAULT NULL,
  `city` varchar(30) CHARACTER SET gb2312 COLLATE gb2312_chinese_ci NULL DEFAULT NULL,
  `state_province` varchar(25) CHARACTER SET gb2312 COLLATE gb2312_chinese_ci NULL DEFAULT NULL,
  `country_id` varchar(2) CHARACTER SET gb2312 COLLATE gb2312_chinese_ci NULL DEFAULT NULL,
  PRIMARY KEY (`location_id`) USING BTREE
) ENGINE = InnoDB AUTO_INCREMENT = 3201 CHARACTER SET = gb2312 COLLATE = gb2312_chinese_ci ROW_FORMAT = Dynamic;

-- ----------------------------
-- Records of locations
-- ----------------------------
INSERT INTO `locations` VALUES (1000, '1297 Via Cola di Rie', '00989', 'Roma', NULL, 'IT');
INSERT INTO `locations` VALUES (1100, '93091 Calle della Testa', '10934', 'Venice', NULL, 'IT');
INSERT INTO `locations` VALUES (1200, '2017 Shinjuku-ku', '1689', 'Tokyo', 'Tokyo Prefecture', 'JP');
INSERT INTO `locations` VALUES (1300, '9450 Kamiya-cho', '6823', 'Hiroshima', NULL, 'JP');
INSERT INTO `locations` VALUES (1400, '2014 Jabberwocky Rd', '26192', 'Southlake', 'Texas', 'US');
INSERT INTO `locations` VALUES (1500, '2011 Interiors Blvd', '99236', 'South San Francisco', 'California', 'US');
INSERT INTO `locations` VALUES (1600, '2007 Zagora St', '50090', 'South Brunswick', 'New Jersey', 'US');
INSERT INTO `locations` VALUES (1700, '2004 Charade Rd', '98199', 'Seattle', 'Washington', 'US');
INSERT INTO `locations` VALUES (1800, '147 Spadina Ave', 'M5V 2L7', 'Toronto', 'Ontario', 'CA');
INSERT INTO `locations` VALUES (1900, '6092 Boxwood St', 'YSW 9T2', 'Whitehorse', 'Yukon', 'CA');
INSERT INTO `locations` VALUES (2000, '40-5-12 Laogianggen', '190518', 'Beijing', NULL, 'CN');
INSERT INTO `locations` VALUES (2100, '1298 Vileparle (E)', '490231', 'Bombay', 'Maharashtra', 'IN');
INSERT INTO `locations` VALUES (2200, '12-98 Victoria Street', '2901', 'Sydney', 'New South Wales', 'AU');
INSERT INTO `locations` VALUES (2300, '198 Clementi North', '540198', 'Singapore', NULL, 'SG');
INSERT INTO `locations` VALUES (2400, '8204 Arthur St', NULL, 'London', NULL, 'UK');
INSERT INTO `locations` VALUES (2500, 'Magdalen Centre, The Oxford Science Park', 'OX9 9ZB', 'Oxford', 'Oxford', 'UK');
INSERT INTO `locations` VALUES (2600, '9702 Chester Road', '09629850293', 'Stretford', 'Manchester', 'UK');
INSERT INTO `locations` VALUES (2700, 'Schwanthalerstr. 7031', '80925', 'Munich', 'Bavaria', 'DE');
INSERT INTO `locations` VALUES (2800, 'Rua Frei Caneca 1360 ', '01307-002', 'Sao Paulo', 'Sao Paulo', 'BR');
INSERT INTO `locations` VALUES (2900, '20 Rue des Corps-Saints', '1730', 'Geneva', 'Geneve', 'CH');
INSERT INTO `locations` VALUES (3000, 'Murtenstrasse 921', '3095', 'Bern', 'BE', 'CH');
INSERT INTO `locations` VALUES (3100, 'Pieter Breughelstraat 837', '3029SK', 'Utrecht', 'Utrecht', 'NL');
INSERT INTO `locations` VALUES (3200, 'Mariano Escobedo 9991', '11932', 'Mexico City', 'Distrito Federal,', 'MX');

SET FOREIGN_KEY_CHECKS = 1;

查询常量

select 常量值 

注意：字符型和容器型的常量值必须用单引号引起来，数值型不需要

查询函数

select 函数名(实参列表)

查询方式

select 00/12

起别名的两种方式

1：使用 as 的方式起别名

 select name as username from user

2：使用空格的方式起别名

select name 	username from user

进阶1：基础查询

语法：

select 	查询列表  	from 	表明;

特点：

1：查询列表可以是：表中的字段，常量值，表达式，函数

2：查询的结果是一个虚拟的表格

去重的使用 distinct

例如：select distinct department_id from employees;

案例查询员工表中涉及到的所有表的所有部门的编号

SELECT DISTINCT
department_id 
FROM
employees;

+号的作用

java中的+作用

1：运算符，两个操作数都为数值型

2：连接符，只要有一个操作数为字符串

mysql中 的+号：

仅仅只有一个功能：运算符

		select 12+9;  两个操作数都为数值型，则做加法运算
		
		select '234'+122; 只要其中一方为字符型，视图将字符型数值转换成数值型，如果转换成功，则继续做加法运算
		
		select 'yayuan'+20;如果转换失败，则将字符型数值转换为0

select null+2;只要其中一方为null,则结果肯定为null

使用CONCAT函数进行连接

CONCAT(str1,str2,...)函数是字符串拼接,如果里面的字符有null，则查询的结果为null

SELECT
	CONCAT( 'a', 'b' ) AS 结果;

案例，查询员工名和姓连接成一个字段，并显示为姓名

SELECT
	CONCAT( last_name, first_name ) 姓名 
FROM
	employees;

IFNULL函数

IFNULL函数功能：

判断字段或表达式是否为Null，如果为null,返回指定的值，否则返回具体的值

IFNULL(expr1,expr2) 函数表示 如果expr1为null,那么使用expr2来代替expr1的值

SELECT
	IFNULL( commission_pct, 0 ) AS 奖金率,
	commission_pct 
FROM
	employees;

isnull函数

功能：判断某字段或表达式是否为Null，如果是，则返回1，否则返回0

显示出表employees的部分列，各个列之间用逗号连接,列头显示 OUT_PUT

SELECT
	CONCAT(
		`first_name`,
		',',
		`last_name`,
		',',
		`job_id`,
		',',
	IFNULL( commission_pct, 0 )) AS "OUT_PUT" 
FROM
	employees;