類型轉換和其他函數
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;
Fm 去0
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;
練習：
查詢2006年入職員工：
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;
--不推薦
select last_name
from employees
where hire_date like ‘2006%‘;
查詢歷年9月份入職的員工：
select last_name
from employees
where to_char(hire_date, ‘mm‘)=‘09‘;
select last_name
from employees
where extract(month from hire_date)=9;
其他函數：
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;
練習：
顯示所有員工部門編號，沒有部門的顯示“未分配部門”
case和decode：
IT_PROG +1000
SA_REP +1500
ST_CLERK +2000
其他人工資不變
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;
練習：
按照員工工資，對員工分級顯示：
A 20001-25000
B 15001-20000
C 10001-15000
D 5001-10000
E 0-5000
類型轉換和其他函數