【1】 LOWER : 将字符串中的内容全部转成小写
UPPER : 将字符串中的内容全部转成大写
SELECT LOWER ('abAcD')
FROM DUAL
SELECT UPPER('abAcd')
FROM DUAL
SELECT UPPER(first_name)
FROM employees
【2】CONCAT : 字符串拼接
SUBSTR :截取子串,从2的位置开始偏移量为3
LENGTH :长度
CONCAT('Hello', 'World') HelloWorld
SUBSTR('HelloWorld',1,5) Hello
LENGTH('HelloWorld') 10
INSTR('HelloWorld', 'W') 6
LPAD(salary,10,'*') *****24000
RPAD(salary, 10, '*') 24000*****
TRIM('H' FROM 'HelloWorld') elloWorld
REPLACE('abcd','b','m') amcd
【3】 LPAD (右对齐)| RPAD (左对齐):
TRIM : 清除字符串左右两端指定的字符
REPLACE : 替换字符串中指定的某个字符
SELECT CONCAT ('aaa','bbb','ccc')abc
FROM DUAL
SELECT CONCAT(first_name,'',last_name) NAME
FROM employees
【4】mysql的索引值是从1开始的,截取子串,从2的位置开始偏移量为3
SELECT SUBSTR('HelloMysql',2,3)
FROM DUAL
SELECT LENGTH('Hello')
FROM DUAL
SELECT INSTR('hellolo','lo')
FROM DUAL
SELECT LPAD(first_name,10,'')
FROM employees
SELECT TRIM(''FROM 'abc de')
FROM DUAL
SELECT TRIM('#' FROM '####abc de#####')
FROM DUAL
SELECT REPLACE('abcdef','a','A')
FROM DUAL
【5】数字函数
ROUND: 四舍五入
ROUND(45.926, 2) 45.93
TRUNCATE: 截断
TRUNCATE(45.926) 45
MOD: 求余
MOD(1600, 300) 100
SELECT ROUND(123.65,1) ,ROUND(123.53,0),ROUND(123.43,-1)
FROM DUAL
SELECT TRUNCATE(123.65,1),TRUNCATE(123.53,0),TRUNCATE(123.53,-1)
FROM DUAL
SELECT MOD(5,3),MOD(-5,3),MOD(5,-3),MOD(-5,-3)
FROM DUAL
【6】 日期函数 now() : 获取当前时间
SELECT NOW()
FROM DUAL
【7】 通用函数 : ifnull
注意 :null和其它值做运算结果仍为null
SELECT employee_id,salary,12*salary*(1+commission_pct)
FROM employees;
SELECT salary,commission_pct,salary * commission_pct
FROM employees
WHERE employee_id =100
【8】 IFNull(commission_pct,0) :如果commission_pct 的值为null那么就将值设置为0
SELECT employee_id,salary,12*salary*(1 + IFNULL(commission_pct,0))
FROM employees
WHERE employee_id = 100
【11】 练习:查询部门号为 10, 20, 30 的员工信息, 若部门号为 10,
则打印其工资的 1.1 倍, 20 号部门, 则打印其工资的 1.2 倍,
30 号部门打印其工资的 1.3 倍数
SELECT first_name,salary,department_id,
CASE department_id
WHEN 10 THEN salary * 1.1
WHEN 20 THEN salary * 1.2
WHEN 30 THEN salary * 1.3
ELSE salary * 1.4 END new_salary
FROM employees
SELECT first_name,salary,job_id,
CASE job_id
WHEN 'IT_PROG' THEN salary*2
ELSE salary *1.4 END new_salary
FROM employees
【12】 AVG() : 求平均值
SUM() :求和
MAX() : 求最大值
MIN() : 求最小值
COUNT() : 求个数
-- avg只能运算数值(double,int)
SELECT AVG(salary)
FROM employees
SELECT SUM(salary)
FROM employees
-- max,min 可以运算数值,字符串,日期
SELECT MAX(first_name),MAX(salary)
FROM employees
SELECT MIN(first_name),MIN(salary)
FROM employees
【13】count:统计的个数不包含数值为null
SELECT COUNT(salary),COUNT(commission_pct)
FROM employeesSELECT AVG(salary),SUM(salary)/107,SUM(salary)/COUNT(commission_pct)
FROM employees
【14】 需求:求表中的数据有多少
SELECT COUNT(*),COUNT(1),COUNT(2)
FROM employeesSELECT first_name
FROM employees
WHERE 1 =1; -- 可以理解为没有条件
【15】 group by
① 需求:求所有员工的平均工资
SELECT AVG(salary)
FROM employees
-- 下面的写法是错误的
SELECT first_name,AVG(salary)
FROM employees
② 需求: 求各部门员工的平局工资
如果列中出现了组函数和其他的列。那么其他的列必须作为
group by 后面分组的条件
SELECT department_id,AVG(salary)
FROM employees
-- group by 按照什么样的格式来分组
GROUP BY department_id
③需求:求各部门中不同工种的员工的平均工资
SELECT department_id, job_id,AVG(salary)
FROM employees
GROUP BY department_id,job_id
SELECT department_id, job_id,AVG(salary)
FROM employees
-- group by 后面的两个列交换顺序是没有区别的
GROUP BY job_id,department_id
【16】 having
①需求 :求各个部门中最高工资大于10000的部门
-- 注意 :如果过滤条件中出现了组函数,那么只能放在having后面使用
SELECT department_id,MAX(salary)
FROM employees
GROUP BY department_id
HAVING MAX(salary)>10000
②需求:求 20,30,40部门中最高工资大于10000的部门
SELECT department_id,MAX(salary)
FROM employees
GROUP BY department_id
HAVING MAX (salary)>10000 AND department_id IN (20,30,40)
-- 下面的方式比上面的好
SELECT department_id,MAX(salary)
FROM employees
WHERE department_id IN(20,30,40)
GROUP BY department_id
HAVING MAX(salary)>10000
DESC customers
INSERT INTO customers(NAME,email,birth) VALUES('鲁宾','[email protected]','1196-02-56')