条件表达式 ：IF-THEN-ELSE 逻辑

CASE expr WHEN comparison_expr1 THEN return_expr1

???????? [WHEN comparison_expr2 THEN return_expr2

????????? WHEN comparison_exprn THEN return_exprn

????????? ELSE else_expr]

END

?

DECODE(col|expression, search1, result1

????? ?????????? ???[, search2, result2,...,]

????? ?????????? ???[, default])

?

//为职位是Manager的员工发放5000元的奖金

SQL> select ename,job,case job when 'MANAGER' then nvl(sal,0)+5000? end? as "工资" from emp;

//员工的工资

SQL> select ename ,job,

? 2? case job when 'MANAGER' then nvl(sal,0)+5000+nvl(comm,0)

? 3? else nvl(sal,0)+nvl(comm,0)

? 4? end

? 5? from emp;

//改写成 decode的写法

SQL> select ename,job

? 2? ,decode(job,'MANAGER', nvl(sal,0)+5000+nvl(comm,0),