Oracle第五天 函数

单行函数

Count            计数
Distinct          除去重复
Commission         奖金
Group by          分组
Department         部门
Job             职位

SQL> select upper(first_name), lower(last_name), length(last_name) from employees;

 

SQL> select (sysdate-hire_date)/7 from employees;

SQL> select trunc((sysdate-hire_date)/30, 0) from employees;

SQL> select trunc(months_between(sysdate,hire_date), 0) from employees;

SQL> select sysdate+3650 from dual;

SQL> select add_months(sysdate, 120) from dual;

SQL> select next_day('2015-09-01', 'friday') from dual;

SQL> select next_day('2015-10-01', 6) from dual;

SQL> select last_day(sysdate) from dual;

 

SQL> select round(to_date('2015-10-10','yyyy-mm-dd'), 'MONTH') from dual;

SQL> select round(to_date('2015-10-16','yyyy-mm-dd'), 'MONTH') from dual;

SQL> select round(to_date('2015-10-10','yyyy-mm-dd'), 'YEAR') from dual;

SQL> select round(sysdate, 'DAY') from dual;

 

练习：

找出各月最后三天内受雇的所有雇员

extract(month from hire_date+4) != extract(month from hire_date)

找出早于25年之前受雇的雇员

months_between(sysdate, hire_date)/300>=25

显示正好为6个字符的雇员姓名

length(last_name)=6

显示所有雇员的姓名的前三个字符

substr(last_name, 1, 3)

显示所有雇员的姓名，用a替换所有'A'

replace(last_name, 'A', 'a')

类型转换和其他函数

SQL> select to_char(salary, '$999,999.00') from employees;

SQL> select last_name, to_char(hire_date, 'dd-Mon-RR') from employees;

SQL> select to_char(sysdate, 'yyyy-mm-dd hh24:mi:ss') from dual;

SQL> select to_char(sysdate, 'yyyy-mm-dd hh:mi:ss AM') from dual;

SQL> select last_name from employees where hire_date=to_date('2006-05-23', 'yyyy-mm-dd');

SQL> select to_number('$123,456.78', '$999,999.00') from dual;

 

练习：

查询2006年入职员工：

select last_name

from employees

where hire_date between to_date('2006-01-01', 'yyyy-mm-dd')

and  to_date('2006-12-31', 'yyyy-mm-dd');

 

select last_name

from employees

where to_char(hire_date, 'yyyy')='2006';

 

select last_name

from employees

where extract(year from hire_date)=2006;

 

--不推荐

select last_name

from employees

where hire_date like '2006%';

 

查询历年9月份入职的员工：

select last_name

from employees

where to_char(hire_date, 'mm')='09';

 

select last_name

from employees

where extract(month from hire_date)=9;

 

其他函数：

nvl：

nvl(val1, val2)

if val1 is not null

then

    return val1;

else

    return val2;

SQL> select last_name, salary*12*(1+nvl(commission_pct, 0)) total_salary from employees;

 

练习：

显示所有员工部门编号，没有部门的显示“未分配部门”

 

case和decode：

IT_PROG +1000

SA_REP +1500

ST_CLERK +2000

其他人工资不变

 

select salary+1000 from employees where job_id='IT_PROG';

 

select last_name, job_id, salary,

case job_id

  when 'IT_PROG' then salary+1000

  when 'SA_REP' then salary+1500

  when 'ST_CLERK' then salary+2000

  else salary

end new_salary

from employees;

 

select last_name, job_id, salary,

decode( job_id,

  'IT_PROG', salary+1000,

  'SA_REP',  salary+1500,

  'ST_CLERK', salary+2000,

  salary) new_salary

from employees;

练习：

按照员工工资，对员工分级显示：

A 20001-25000

B 15001-20000

C 10001-15000

D 5001-10000

E 0-5000

分组函数

Count            计数
Distinct          除去重复
Commission         奖金
Group by          分组
Department         部门
Job             职位

 

 

SQL> select count(*), sum(salary), avg(salary), min(salary), max(salary) from employees;

 

SQL> create table t1(x int);

SQL> insert into t1 values (null);

SQL> insert into t1 values (1);

SQL> commit;

SQL>       count（*）对行做统计

SQL> select count(x) from t1;

SQL> select max(x) from t1;

SQL> select min(x) from t1;

SQL> select sum(x) from t1;

SQL> select avg(x) from t1;

 

SQL> select avg(salary), avg(nvl(commission_pct, 0)) from employees;

SQL> select count(distinct department_id) from employees; 去除重复值

 

Group by分组：

SQL> select department_id, avg(salary) from employees group by department_id;

多列分组：

SQL> select department_id, job_id, max(salary) from employees group by department_id, job_id;

SQL> select department_id, job_id, max(salary), last_name from employees group by department_id, job_id; 错误语法

 

练习：

公司中不同职位的数量     SQL> select count(distinct job_id) from employees;

 

计算每个部门的人数

SQL> select department_id,count(employee_id) 人数

  2  from employees

  3  group by department_id;

 

按年份分组，求员工的工资总和

SQL>select  extract(year from hire_date),avg(salary)

from employees

group by extract(year from hire_date)

 

Having语句：

SQL> select department_id, avg(salary) from employees where avg(salary)>=5000 group by department_id; 错误语句

SQL> select department_id, avg(salary) from employees group by department_id having avg(salary)>=5000;

 

练习：

按部门求出所有有部门的普通员工的平均工资，部门平均工资少于5000的不显示，最终结果按平均工资的降序排列。

select department_id, avg(salary) avg_sal

from employees

where job_id not like '%\_MGR' escape '\' and department_id is not null

group by department_id

having avg(salary)>=5000

order by avg_sal desc;