Oracle基础操作入门

select语句

--选择全部列
select * from departments;
--选择特定列
select department_id,department_name from departments;
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算数运算符(+ - * /)

--使用数学运算符，规则如下：
--乘除的优先级高于加减
--同一优先级运算符从左向右执行
--括号内的运算先执行
select last_name,salary,salary+300 from employees;
select last_name,salary,salary*12+100 from employees;
select last_name,salary,(salary+100)*12 from employees;
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定义空值

--空值是无效的，未指定的，未知的或不可预知的值
--空值不是空格或者0
select last_name,job_id,salary,commission_pct from employees;
--空值在数学运算中的使用
--包含空值的数字表达式的值都为空值
--select last_name,job_id,salary*12*commission_pct from employees;
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列的别名

--重命名一个列,紧跟列名，也可以在列名和别名之间加入关键字'AS'
--别名使用双引号，以便在别名中包含空格或特殊的字符并区分大小写
select last_name as name,commission_pct comm from employees;
select last_name as "name",commission_pct "comm" from employees;
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连接符

--把列与列，列与字符串连接在一起
--用 || 表示，可以用来合成列
select last_name||job_id as "Employees" from employees;
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字符串

--字符串可以是SELECT列表中的一个字符,数字,日期
--日期和字符只能在单引号中出现
select last_name || ' is a ' || job_id as "Employees Details" from employees;
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重复行

--在SELECT子句中使用关键字"DISTINCT"删除重复行。
select department_id from employees;
select distinct department_id from employees;
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过滤

--使用where子句，将不满足天剑的行过滤掉
--where子句紧随from子句
SELECT
	employee_id,
	last_name,
	job_id,
	department_id
FROM
	employees
WHERE
	department_id = 90;
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字符和日期

--字符和日期要包含在单引号中
--字符大小写敏感，日期格式敏感
--默认的日期格式为DD-MON月-RR  (PL/SQL)
SELECT
	last_name,
	hire_date,
	department_id
FROM
	employees
WHERE
	hire_date = '7-6月-1994';
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比较运算

--常见比较运算符 = > >= < <= <>(!=)
SELECT
	last_name,
	salary
FROM
	employees
WHERE
	salary <= 3000;
	
--其它比较运算
--between...and...  在两个值之间（包含边界）
SELECT
	last_name,
	salary
FROM
	employees
WHERE
	salary BETWEEN 2500
AND 3500;

--in  等于值列表中的一个
SELECT
	employee_id,
	last_name,
	manager_id
FROM
	employees
WHERE
	manager_id IN (100, 101, 201);
	
--like  模糊查询
--%代表零个或多个字符（任意个字符）
--_代表一个字符
SELECT
	first_name
FROM
	employees
WHERE
	first_name LIKE 'S%';

SELECT
	last_name
FROM
	employees
WHERE
	last_name LIKE '_o%';
	
--is null  空值
--is (not) null判断空值
SELECT
	last_name,
	manager_id
FROM
	employees
WHERE
	manager_id IS NULL;
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escape回避特殊符号

--将[%]转为[\%]、[_]转为[\_]，然后再加上[ESCAPE '\'] 即可。
SELECT
	job_id
FROM
	jobs
WHERE
	job_id LIKE 'IT\_%' ESCAPE '\' ;
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逻辑运算

--and  逻辑并，要求并的关系为真
SELECT
	employee_id,
	last_name,
	job_id,
	salary
FROM
	employees
WHERE
	salary >= 10000
AND job_id LIKE '%MAN%';

--or  逻辑或
SELECT
	employee_id,
	last_name,
	job_id,
	salary
FROM
	employees
WHERE
	salary >= 10000
OR job_id LIKE '%MAN%';

--not  逻辑否
SELECT
	last_name,
	job_id
FROM
	employees
WHERE
	job_id NOT IN (
		'IT_PROG',
		'ST_CLERK',
		'SA_REP'
	);
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order by子句

--使用order by子句排序
--ASC：升序  DESC：降序
--order by子句在select语句的结尾
SELECT
	last_name,
	job_id,
	department_id,
	hire_date
FROM
	employees
ORDER BY
	hire_date DESC;
--按别名排序
SELECT
	employee_id,
	last_name,
	salary * 12 annsal
FROM
	employees
ORDER BY
	annsal;
--多个列排序	
SELECT
	last_name,
	department_id,
	salary
FROM
	employees
ORDER BY
	department_id,
	salary DESC;
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单行函数

字符函数

--大小写控制函数
--lower('SQL Course')------result:sql course
--upper('SQL Course')------result:SQL COURSE
--initcap('SQL Course')------result:Sql Course
SELECT
	employee_id,
	last_name,
	department_id
FROM
	employees
WHERE
	LOWER (last_name) = 'higgins';

--字符控制函数
--concat('Hello','World')------result:HelloWorld
--substr('HelloWorld',1,5)------result:Hello
--  substr下标从1开始，截取5个字符
--length('HelloWorld')------result:10
--instr('HelloWorld','W')------result:6
  从左到右查找字符第一次出现的位置，下标从0开始
--lpad(salary,10,*)------result:*****24000
--rpad(salary,10,*)------result:24000*****
--trim('H' from 'HelloWorld')------result:elloWorld
--  去除'HelloWorld'两边出现的'H'字符
--replace('abcd','b','m')------amcd
--  把abcd中所有的b都替换成m
SELECT
	employee_id,
	CONCAT (first_name, last_name) NAME,
	job_id,
	LENGTH (last_name),
	INSTR (last_name, 'a')
FROM
	employees
WHERE
	SUBSTR (job_id, 4) = 'REP';
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数值函数

--round(45.9262,2):四舍五入 45.93
--trunc(45.9262,2)：截断 45.92
--mod(1600,300):求余 100
SELECT
	last_name,
	salary,
	MOD (salary, 5000)
FROM
	employees
WHERE
	job_id = 'SA_REP';
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日期函数

--oracle中的日期型数据实际含有两个值：日期和时间
--日期的数学运算
SELECT
	last_name,
	(SYSDATE - hire_date) / 7 AS weeks
FROM
	employees
WHERE
	department_id = 90;

--日期函数
--months_between------两个日期相差的月数
SELECT
	MONTHS_BETWEEN (
		'6-7月-1995',
		'11-11月-1994'
	)
FROM
	dual;
--add_months------向指定日期中加上若干月数
SELECT
	ADD_MONTHS ('6-7月-1995', 6)
FROM
	dual;
--next_day------指定日期的下一个星期*对应的日期
--星期日一二三四五六所代表的数字为1234567
SELECT
	NEXT_DAY ('26-10月-2018', 7)
FROM
	dual;
--last_day------本月的最后一天
SELECT
	LAST_DAY ('26-10月-2018')
FROM
	dual;
--round------日期的四舍五入
round(sysdate,'month')------2018-11-01
round(sysdate,'year')------2019-01-01
--trunc------日期截断
trunc(sysdate,'month')------2018-10-01
trunc(sysdate,'year')------2018-01-01
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转换函数

--隐式数据类型转换(oracle自动完成转换)
> varchar2--->number
> varchar2--->date
> number--->varchar2
> date--->varchar2
--显式数据类型转换
--to_char函数对日期的转换(to_char(date,format_model))
SELECT
	TO_CHAR (
		SYSDATE,
		'yyyy-mm-dd hh24:mi:ss'
	)
FROM
	dual;
--to_date函数对字符的转换(to_date(char,format_model))
--格式必须匹配
SELECT
	TO_DATE (
		'2018年10月26日08:10:21',
		'yyyy"年"mm"月"dd"日"hh24:mi:ss'
	)
FROM
	dual;
--to_char函数对数字的转换(to_char(number,format_model))
--很少会用到
--to_number函数对字符的转换(to_number(char,format_model))
--很少会用到
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通用函数

--适用于任何数据类型，同时也是用于空值
--nvl(expr1,expr2):将空值转换成一个已知的值
--可以使用的数据类型有日期、字符、数字
SELECT
	last_name,
	salary,
	NVL (commission_pct, 0),
	(salary * 12) + (
		salary * 12 * NVL (commission_pct, 0)
	) an_sal
FROM
	employees;
	
--nvl2(expr1,expr2,expr3)
--若expr1不为null，返回expr2，否则返回expr3
SELECT
	last_name,
	salary,
	commission_pct,
	NVL2 (
		commission_pct,
		'sal+comm',
		'sal'
	) income
FROM
	employees
WHERE
	department_id IN (50, 80);
	
--nullif(expr1,expr2)
--相等返回null，不等返回expr1
SELECT
	first_name,
	LENGTH (first_name) "expr1",
	last_name,
	LENGTH (last_name) "expr2",
	NULLIF (
		LENGTH (first_name),
		LENGTH (last_name)
	) result
FROM
	employees;
	
--coalesce(expr1,expr2,...,exprn)
--coalesce与nvl相比的优点在于coalesce可以同时处理交替的多个值
--如果第一个表达式为空则返回下一个表达式，对其他的参数进行coalesce
SELECT
	last_name,
	COALESCE (commission_pct, salary, 10) comm
FROM
	employees
ORDER BY
	commission_pct;
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条件表达式

--类似于sql语句中的if-then-else逻辑
--case表达式
SELECT
	last_name,
	job_id,
	salary,
	CASE job_id
WHEN 'IT_PROG' THEN
	1.10 * salary
WHEN 'ST_CLERK' THEN
	1.15 * salary
WHEN 'SA_REP' THEN
	1.20 * salary
ELSE
	salary
END "revised_salary"
FROM
	employees;
--decode函数
SELECT
	last_name,
	job_id,
	salary,
	DECODE (
		job_id,
		'IT_PROG',
		1.10 * salary,
		'ST_CLERK',
		1.15 * salary,
		'SA_REP',
		1.20 * salary,
		salary
	) "revised_salary"
FROM
	employees;
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嵌套函数

单行函数可以嵌套
嵌套函数的执行顺序是由内到外
SELECT
	last_name,
	NVL (
		TO_CHAR (manager_id),
		'No Manager'
	)
FROM
	employees
WHERE
	manager_id IS NULL;
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多表查询

在where子句中写入连接条件
在表中有相同列时，在列名之前加上表名前缀

等值连接

--连接n个表，至少需要n-1个连接条件
SELECT
	E .employee_id,
	E .last_name,
	E .department_id,
	D .department_id,
	D .location_id
FROM
	employees E,
	departments D
WHERE
	E .department_id = D .department_id;
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非等值连接

SELECT
	E .last_name,
	E .salary,
	j.grade_level
FROM
	employees E,
	job_grades j
WHERE
	E .salary BETWEEN j.lowest_sal
AND j.highest_sal;
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外连接

--连接条件中没有匹配行的表的列后面要加外连接运算符(+)
--左外连接：除了返回满足条件的数据外，还返回左表中不满足条件的数据
SELECT
	E .last_name,
	E .department_id,
	D .department_name
FROM
	employees E,
	departments D
WHERE
	E .department_id = D .department_id (+);
--右外连接：除了返回满足条件的数据外，还返回右表中不满足条件的数据
SELECT
	E .last_name,
	E .department_id,
	D .department_name
FROM
	employees E,
	departments D
WHERE
	E .department_id (+) = D .department_id;
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自连接

--自连接
SELECT
	M .*
FROM
	employees E,
	employees M
WHERE
	M .employee_id = E .manager_id
AND LOWER (E .last_name) = 'chen';
--子查询
SELECT
	*
FROM
	EMPLOYEES
WHERE
	EMPLOYEE_ID = (
		SELECT
			MANAGER_ID
		FROM
			EMPLOYEES
		WHERE
			LOWER (LAST_NAME) = 'chen'
	)
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使用on子句创建连接(常用)

--内连接
SELECT
	E .employee_id,
	E .last_name,
	E .department_id,
	D .department_id,
	D .location_id
FROM
	employees E
INNER JOIN departments D ON E .department_id = D .department_id;

SELECT
	E .employee_id,
	l.city,
	D .department_name
FROM
	employees E
INNER JOIN departments D ON E .department_id = D .department_id
INNER JOIN locations l ON D .location_id = l.location_id;

--左外连接
SELECT
	E .last_name,
	E .employee_id,
	D .department_name
FROM
	employees E
LEFT OUTER JOIN departments D ON E .department_id = D .department_id;

--右外连接
SELECT
	E .last_name,
	E .employee_id,
	D .department_name
FROM
	employees E
RIGHT OUTER JOIN departments D ON E .department_id = D .department_id;

--满外连接
SELECT
	E .last_name,
	D .department_id,
	D .department_name
FROM
	employees E
FULL OUTER JOIN departments D ON E .department_id = D .department_id;
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分组函数

--分组函数作用于一组数据，并对一组数据返回一个值
--avg(平均值)和sum(合计)函数
--可以对数值型数据使用avg和sum函数
SELECT
	AVG (salary),
	SUM (salary)
FROM
	employees
WHERE
	job_id LIKE '%REP%';
	
--min(最小值)和max(最大值)函数
--可以对任意数据类型的数据使用min和max函数
SELECT
	MIN (hire_date),
	MAX (hire_date)
FROM
	employees;
--count(计数)函数
--count(*)返回表中记录总数，适用于任意数据类型
SELECT
	COUNT (*)
FROM
	employees
WHERE
	department_id = 50;
--count(expr)返回expr不为空的记录总数
SELECT
	COUNT (COMMISSION_PCT)
FROM
	employees;
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组函数忽略空值

SELECT
	AVG (COMMISSION_PCT),
	COUNT (commission_pct),
	SUM (commission_pct),
	SUM (commission_pct) / COUNT (*),
	SUM (commission_pct) / COUNT (commission_pct)
FROM
	employees;
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在组函数中使用nvl函数

--nvl函数使分组函数无法忽略空值
SELECT
	AVG (NVL(commission_pct, 0))
FROM
	employees;
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distinct关键字

--count(distinct expr)返回expr非空且不重复的记录总数
SELECT
	COUNT (DISTINCT department_id)
FROM
	employees;
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group by子句语法

--可以使用group by子句将表中的数据分成若干组
--在select列表中所有未包含在组函数中的列都应该包含在group by子句中
SELECT
	department_id,
	AVG (salary)
FROM
	employees
GROUP BY
	department_id;
	
--包含在group by子句中的列不必包含在select列表中
SELECT
	AVG (salary)
FROM
	employees
GROUP BY
	department_id;
	
--在group by子句中包含多个列
SELECT
	department_id dept_id,
	job_id,
	SUM (salary)
FROM
	employees
GROUP BY
	department_id,
	job_id;
--不能在where子句中使用组函数
--可以在having子句中使用组函数
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过滤分组：having子句

--使用having过滤分组：
--行已经被分组
--使用了组函数
--满足having子句中条件的分组将被显示
SELECT
	department_id,
	MAX (salary)
FROM
	employees
GROUP BY
	department_id
HAVING
	MAX (salary) > 10000;
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嵌套组函数

--显示各部门平均工资的最大值
SELECT
	MAX (AVG(salary))
FROM
	employees
GROUP BY
	department_id;
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子查询

--子查询(内查询)在主查询之前一次执行完成
--子查询的结果被主查询(外查询)使用
SELECT
	last_name
FROM
	employees
WHERE
	salary > (
		SELECT
			salary
		FROM
			employees
		WHERE
			last_name = 'Abel'
	);

--单行子查询：只返回一行
--操作符：=  >  >=  <  <=  <>
--返回job_id与141号员工相同，salary比143号员工多的员工
--  姓名，job_id 和工资
SELECT
	last_name,
	job_id,
	salary
FROM
	employees
WHERE
	job_id = (
		SELECT
			job_id
		FROM
			employees
		WHERE
			employee_id = 141
	)
AND salary > (
	SELECT
		salary
	FROM
		employees
	WHERE
		employee_id = 143
);

--返回公司工资最少的员工的last_name,job_id和salary
SELECT
	last_name,
	job_id,
	salary
FROM
	employees
WHERE
	salary = (
		SELECT
			MIN (salary)
		FROM
			employees
	);
	
--查询最低工资大于50号部门最低工资的部门id和其最低工资
SELECT
	department_id,
	MIN (salary)
FROM
	employees
GROUP BY
	department_id
HAVING
	MIN (salary) > (
		SELECT
			MIN (salary)
		FROM
			employees
		WHERE
			department_id = 50
	);
	
--多行子查询：返回多行
--操作符：in  any  all
--in:等于列表中的任意一个
--any:和子查询返回的某一个值比较
--返回其它部门中比job_id为'IT_PROG'部门任一工资低的员工的员
--  工号、姓名、job_id 以及salary
SELECT
	employee_id,
	last_name,
	job_id,
	salary
FROM
	employees
WHERE
	salary < ANY (
		SELECT
			salary
		FROM
			employees
		WHERE
			job_id = 'IT_PROG'
	)
AND job_id <> 'IT_PROG';
--all:和子查询返回的所有值比较
--返回其它部门中比job_id为‘IT_PROG’部门所有工资都低的员工
--  的员工号、姓名、job_id 以及salary

SELECT
	employee_id,
	last_name,
	job_id,
	salary
FROM
	employees
WHERE
	salary < ALL (
		SELECT
			salary
		FROM
			employees
		WHERE
			job_id = 'IT_PROG'
	)
AND job_id <> 'IT_PROG';

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子查询中的空值问题

SELECT
	last_name,
	job_id
FROM
	employees
WHERE
	job_id = (
		SELECT
			job_id
		FROM
			employees
		WHERE
			last_name = 'Haas'
	);
--no rows selected
--子查询不反回任何行
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1、查询每个月倒数第2天入职的员工的信息

SELECT
	last_name,
	hire_date
FROM
	employees
WHERE
	hire_date = LAST_DAY (hire_date) - 1
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2、查询出 last_name 为 'Chen' 的 manager 的信息.

SELECT
	*
FROM
	EMPLOYEES
WHERE
	EMPLOYEE_ID = (
		SELECT
			MANAGER_ID
		FROM
			EMPLOYEES
		WHERE
			LOWER (LAST_NAME) = 'chen'
	)
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3、查询平均工资高于 8000 的部门 id 和它的平均工资

SELECT
    department_id,
	AVG (salary)
FROM
	EMPLOYEES
GROUP BY
	DEPARTMENT_ID
HAVING
	AVG (salary) > 8000
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4、查询工资最低的员工信息: last_name, salary

SELECT
	last_name,
	salary
FROM
	employees
WHERE
	SALARY = (
		SELECT
			MIN (salary)
		FROM
			EMPLOYEES
	);
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5、查询平均工资最低的部门信息

SELECT
	*
FROM
	DEPARTMENTS
WHERE
	DEPARTMENT_ID = (
		SELECT
			DEPARTMENT_ID
		FROM
			EMPLOYEES
		GROUP BY
			DEPARTMENT_ID
		HAVING
			AVG (salary) = (
				SELECT
					MIN (AVG(salary))
				FROM
					EMPLOYEES
				GROUP BY
					department_id
			)
	)
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6、查询平均工资最低的部门信息和该部门的平均工资

SELECT
	D .*, (
		SELECT
			AVG (salary)
		FROM
			EMPLOYEES E
		WHERE
			E .DEPARTMENT_ID = D .DEPARTMENT_ID
	)
FROM
	DEPARTMENTS D
WHERE
	D .DEPARTMENT_ID = (
		SELECT
			DEPARTMENT_ID
		FROM
			EMPLOYEES
		GROUP BY
			DEPARTMENT_ID
		HAVING
			AVG (salary) = (
				SELECT
					MIN (AVG(salary))
				FROM
					EMPLOYEES
				GROUP BY
					DEPARTMENT_ID
			)
	)

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7、查询平均工资最高的 job 信息

SELECT
	*
FROM
	JOBS
WHERE
	job_id = (
		SELECT
			JOB_ID
		FROM
			EMPLOYEES
		GROUP BY
			JOB_ID
		HAVING
			AVG (SALARY) = (
				SELECT
					MAX (AVG(salary))
				FROM
					EMPLOYEES
				GROUP BY
					job_id
			)
	)
复制代码

8、查询平均工资高于公司平均工资的部门有哪些?

SELECT
	department_id
FROM
	EMPLOYEES
GROUP BY
	DEPARTMENT_ID
HAVING
	AVG (salary) > (
		SELECT
			AVG (salary)
		FROM
			EMPLOYEES
	)
复制代码

9、查询出公司中所有 manager 的详细信息

SELECT
	*
FROM
	EMPLOYEES
WHERE
	EMPLOYEE_ID IN (
		SELECT DISTINCT
			manager_id
		FROM
			EMPLOYEES
	);
复制代码

10、各个部门中最高工资中最低的那个部门的最低工资是多少

SELECT
	MIN (salary)
FROM
	EMPLOYEES
WHERE
	DEPARTMENT_ID = (
		SELECT
			DEPARTMENT_ID
		FROM
			EMPLOYEES
		GROUP BY
			DEPARTMENT_ID
		HAVING
			MAX (SALARY) = (
				SELECT
					MIN (MAX(salary))
				FROM
					EMPLOYEES
				GROUP BY
					DEPARTMENT_ID
			)
	)
复制代码

11、查询平均工资最高的部门的 manager 的详细信息: last_name, department_id, email, salary

SELECT
	last_name,
	DEPARTMENT_id,
	email,
	salary
FROM
	EMPLOYEES
WHERE
	EMPLOYEE_ID IN (
		SELECT
			MANAGER_ID
		FROM
			EMPLOYEES
		WHERE
			DEPARTMENT_ID = (
				SELECT
					DEPARTMENT_ID
				FROM
					EMPLOYEES
				GROUP BY
					DEPARTMENT_ID
				HAVING
					AVG (salary) = (
						SELECT
							MAX (AVG(salary))
						FROM
							EMPLOYEES
						GROUP BY
							DEPARTMENT_ID
					)
			)
	)
复制代码

12、查询 1999 年来公司的人所有员工的最高工资的那个员工的信息

SELECT
	*
FROM
	EMPLOYEES
WHERE
	TO_CHAR (HIRE_DATE, 'yyyy') = '1999'
AND SALARY = (
	SELECT
		MAX (salary)
	FROM
		EMPLOYEES
	WHERE
		TO_CHAR (HIRE_DATE, 'yyyy') = '1999'
)
复制代码

13、返回其它部门中比 job_id 为‘IT_PROG’部门所有工资都低的员工的员工号、姓名、job_id 以及 salary

SELECT
	employee_id,
	last_name,
	job_id,
	salary
FROM
	employees
WHERE
	salary < ALL (
		SELECT
			salary
		FROM
			employees
		WHERE
			LOWER (JOB_ID) = 'it_prog'
	)
AND LOWER (JOB_ID) <> 'it_prog';
复制代码

Oracle基础操作入门

select语句

算数运算符(+ - * /)

定义空值

列的别名

连接符

字符串

重复行

过滤

字符和日期

比较运算

escape回避特殊符号

逻辑运算

order by子句

单行函数

字符函数

数值函数

日期函数

转换函数

通用函数

条件表达式

嵌套函数

多表查询

等值连接

非等值连接

外连接

自连接

使用on子句创建连接(常用)

分组函数

组函数忽略空值

在组函数中使用nvl函数

distinct关键字

group by子句语法

过滤分组：having子句

嵌套组函数

子查询

子查询中的空值问题

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