SQL语法体系学习笔记
SQL语法之基础查询（进阶1）and条件查询（进阶2）
SQL语法之排序查询（进阶3）and常见函数（进阶4）
SQL语法之分组函数，分组查询（进阶5）and连接查询（sql92语法进阶6）
进阶1：
基础查询
语法：
select 查询列表 from 表名;
特点：
- 查询的列表可以使：表中的字段，常量值，表达式，函数
- 查询的结果是一个虚拟的表格
举例：
1. 查询表中的单个字段
select last_name from employees;
2. 查询表中的多个字段
SELECT last_name,salary,email FROM employees;
3. 查询表中的所有字段
select * from employee
提醒一下，这里是着重号，并非单引号，用于区分是字段还是关键字，有着重号的话代表是我们所写的字段，也就是键盘esc下方这个按键
4. SQL里面不区分字符和字符串
SELECT 100;
SELECT 'join';
5. 查询表达式
select 100%98;
6. 查询函数
select version();
起别名：
方式一：使用AS
SELECT 100%98 AS 结果;
select last_name AS 姓，first_name AS 名 FROM employees;
(这里的last_name和first_name是原来的列名)
方式二：使用空格
select last_name 姓,first_name 名 FROM employees;
注意
如果别名中有特殊符号的（例如 空格 或者 #号），这个时候需要把别名加上 “ ”或者 ’ ’
错误示范：
SELECT last_name 小 彪 彪,first_name 名 FROM employees;
SELECT last_name '小 彪 彪',first_name 名 FROM employees;
去重：
在我们所需查找的列名前面加个distinct即可
SELECT department_id FROM employees;
select distinct department_id from employees;
+号作用：
java中的+号：
- 运算符，两个操作数都为数值型
- 连接符，只要有一个操作数为字符串即可
MYSQL中的+号：
- 仅仅只只有一个功能：运算符
情况1
两个操作数都为数值型，则作加法运算
SELECT 90+20;
情况2
只要其中一方为字符型时，试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，如果转换失败，则将字符型数值转换成0
SELECT '123'+90;
select 'jhon'+90;
情况3
只要其中一方为null，则结果肯定为null
SELECT NULL+10;
拼接
在mysql中，字符的拼接并非用+号，而使用concat函数
SELECT CONCAT('a','b','c') AS 结果;
进阶查询1数据库初始化代码：
DROP TABLE IF EXISTS `employees`;
CREATE TABLE `employees` (
`employee_id` INT(6) ,
`first_name` VARCHAR(20) ,
`last_name` VARCHAR(25) ,
`email` VARCHAR(25) ,
`phone_number` VARCHAR(20) ,
`job_id` VARCHAR(10) ,
`salary` DOUBLE(10, 2) ,
`commission_pct` DOUBLE(4,2) ,
`manager_id` INT(6) ,
`department_id` INT(4) ,
`hiredate` DATETIME
);
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');
进阶2：
条件查询
语法：
select 查询列表 from 表名 where 筛选条件
1.按条件表达式查询
条件运算符：
> < =（注意mysql中的等于是= 这个，而不是==） != 或者<> >= <=
2.按逻辑表达式筛选
&& || !
and or not
&& and 两个条件都为true，结果为true，反之为false
|| or 只要有一个条件为true，结果为true，反之为false
! not 如果连接的条件本身为false，结果为true，反之为false
3.模糊查询
like
between and
in
is null
举例
1.按条件表达式查询
案例1：查询工资>12000的员工信息
select * from employees where salary>12000;
案例2: 查询部门编号不等于90号的员工名和部门编号
select last_name ,department_id from employees where department_id<>90;
2.按逻辑表达式筛选
案例一：查询工资z在10000到20000之间的员工名，工资以及奖金
SELECT last_name,salary,commission_pct FROM employees WHERE salary >= 10000 AND salary <=20000;
案例二：查询部门编号不是90到110之间，或者工资高于15000的员工信息
select * from employees where department_id<90 or department_id>110 or salary>15000;
select * from employees where not(department_id>=90 and department_id<=110) or salary>15000;
3.模糊查询
like
一般和通配符搭配使用，
通配符：
%任意多个字符，包含0个字符
_任意单个字符
案例1：查询员工命中包含字符a的员工信息
select * from employees where last_name like '%a%';
案例2：查询员工名中第三个字符为e，第五个字符为a 的员工名和工资
select last_name,salary from employees where last_name like '__e_a%';
案例3：查询员工名中第二个字符为_的员工名
SELECT last_name FROM employees WHERE last_name LIKE '_\_%';
(\是转义符号，默认的)
关键字escape
如果要标识某个符号是转义符，可以用关键字escape
select last_name from employees where last_name like '_$_%' escape '$';
between and
注意点
- 使用between and 可以提高语句的简洁度
- 包含临界值
- 两个临界值不要调换顺序，它直接等价于(
employee_id>=100 and employee_id<=120,如果临界值调换顺序后，就变成了employee_id>=120 and employee_id<=100)
实例：查询员工编号在100~110之间的员工信息，
不使用between and：
select * from employees where employee_id>=100 and employee_id<=120;
使用between and：
select * from employees where employee_id between 100 and 120;
in
作用
用于判断某字段的值是否属于in列表中的某一项
意义
- 使用in提高语句（相对于or）简洁度
- in列表的值类型必须一致或兼容
- 列表中不支持写通配符
实例：查询员工的工种编号是IT_PROG，AD_VP，AD_PRE中的一个员工名和工种编号
未使用in：
select last_name,job_id from employees where job_id='IT_PROT' or job_id='AD_VP' or JOB_ID='AD_PRES';
使用in：
select last_name,job_id from employees where job_id in('IT_PROT','AD_VP' ,'AD_PRES');
错误写法：
select last_name,job_id from employees where job_id in('IT_PROT','AD_%');
is null
注意：
- is不能和其它使用进行判断
- =或者<>不能用于判断null值
- is null 或is not null 可以判断null值
案例一：查询没有奖金的员工名和奖金率
错误写法：（=号不能判断null）：
SELECT last_name,commission_pct FROM employees WHERE commission_pct=NULL;
正确写法：
SELECT last_name,commission_pct FROM employees WHERE commission_pct IS NULL;
相反写法：
select last_name,commission_pct from employees where commission_pct is not null;
安全等于<=>
作用
is null：仅仅可以判断null值，建议使用
<=>:既可以判断null值，又可以判断普通的数值可读性较低。
select last_name,department_id,salary*12*(1+ifnull(commission_pct,0)) AS 年薪 from employees;
案例一：查询没有奖金的员工名和奖金率
select last_name,commission_pct from employees where commission_pct <=>null;
案例二：查询工资为12000的员工信息
select last_name,salary from employees where salary <=>12000;
章节测试题
第一题
查询没有奖金，且工资小于18000的salary，last_name
select salary,last_name from employees where commission_pct is null and salary<18000;
第二题
查询employees表中，job_id不为’IT’或者工资为12000的员工信息
select * from employees where job_id <>'IT' or salary=12000;
select * from employees where not(job_id ='IT') or salary=12000;
注意：
(不能用 job_id is not ‘IT’（is not 只能和null连用）)
第三题（经典面试题）
试问：select * from employees ; 和 select * from employees where commission_pct like '%%' and last_name like '%%'结果是否一样？并说明原因
select * from employees ;
SELECT * FROM employees WHERE commission_pct LIKE '%%' AND last_name LIKE '%%';
不一样！
如果判断的字段有null值，那么就不一样
如果把and换成or那么就可以了，因为一行中，不可能全都为null
select * from employees where commission_pct like '%%' or last_name like '%%';
