Oracle_071_lesson_p5
转换函数to_char
to_number
to_date
隐式转换 fm去掉前导0
显式转换 fx 完全精确匹配才会成功，否则报错
NVL(A,B) 若A为NULL，则输出B
select last_name,salary,NVL(commission_pct,0),(salary12)+(salary12*NVL(commission_pct,0)) AN_SAL
from employees;
NVL2(A,B,C) 若A为NULL，则输出C，若A不为NULL，则输出B
select last_name,salary,commission_pct,NVL2(commission_pct,'SAL+COM','SAL') income
from employee where department_id IN (50,80);
NULLIF(A,B) 若A=B，则为NULL，若AB，则输出A
select first_name,LENGTH(first_name) "expr1",last_name,LENGTH(last_name) "expr2",NULLIF(LENGTH(first_name),LENGTH(last_name)) result
from employees;
COALESCE(A,B,C,.......Z) 从A开始往后判断是否为NULL，找到不为NULL时则输出值，单最后Z不能设定为NULL
select last_name,salary,commission_pct,COALESCE((salary+(commission_pct*salary)),salary+2000) "new Salary"
from employees;
条件表达式
CASE
select last_name,job_id,salary,
case job_id when 'IT_PROG' THEN 1.10salary
when 'ST_CLERK' THEN 1.15salary
when 'SA_REP' THEN 1.20*salary
elsesalary
end "REVISED_SALARY"
from employees;
DECODE
select last_name,job_id,salary,
DECODE(job_id,'IT_PROG',1.10salary,
'ST_CLERK',1.15salary,
'SA_REP' ,1.20*salary,
salary)
REVISED_SALARY
from employees;
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