Oracle基础教程：单行函数—分支函数-mysql教程

简单case实现的是等值比较(表达式在when之前)SQLgt; select ename,sal,case deptno when 10 then

分支结构

decode

if expr1
then
action1
elif expr2
then
action2
...
else
default_action
fi

decode(expr1,search1,result1,search2,result2,...,default)
只能做等值比较

SQL> select ename,deptno,decode(deptno,
10,'AAAA',
20,'BBBB',
'CCCC') from emp order by 2;

ENAME DEPTNO DECO
---------- ---------- ----
CLARK 10 AAAA
KING 10 AAAA
MILLER 10 AAAA
JONES 20 BBBB
FORD 20 BBBB
ADAMS 20 BBBB
SMITH 20 BBBB
SCOTT 20 BBBB
WARD 30 CCCC
TURNER 30 CCCC
ALLEN 30 CCCC
JAMES 30 CCCC
BLAKE 30 CCCC
MARTIN 30 CCCC

14 rows selected.

SQL>

练习:
按部分编号涨工资(只打印) 10号部门涨10% 20号部分涨20% 其他部分涨30%

decode
select ename,sal,deptno,
decode(deptno,10,sal*1.1，，
20,sal*2.1，
sal*3.1)
from emp order by deptno;

简单case

select ename,sal,deptno,
case deptno
when 10 then sal*1.1
when 20 then sal*2.1
else sal*3.1
end
from emp order by deptno;

search case

select ename,sal,deptno,
case when deptno=10 then sal*1.1
when deptno=20 then sal*2.1
else sal*3.1
end
from emp order by deptno;

case

简单
case expr when search1 then result1
when search2 then result2
....
else default_result
end
只能做等值比较

简单case实现的是等值比较(表达式在when之前)
SQL> select ename,sal,case deptno when 10 then 'AAA'
when 20 then 'BBB'
else 'CCC'
end
from emp order by deptno;
SQL>

ENAME SAL CAS
---------- ---------- ---
CLARK 2450 AAA
KING 5000 AAA
MILLER 1300 AAA
JONES 2975 BBB
FORD 3000 BBB
ADAMS 1100 BBB
SMITH 800 BBB
SCOTT 3000 BBB
WARD 1250 CCC
TURNER 1500 CCC
ALLEN 1600 CCC
JAMES 950 CCC
BLAKE 2850 CCC
MARTIN 1250 CCC

14 rows selected.

搜索case实现的是不等值比较(表达式在when之后)

select ename,deptno case when deptno=10 then 'aaa'
when deptno=20 then 'bbb'
else 'ccc'
end
from emp;

SQL> select ename,sal,case when sal<=1000 then sal+1
when sal>1000 and sal<=2000 then sal+2
when sal>2000 and sal<=3000 then sal+3
else sal+4
end "up_sal"
from emp order by sal;

ENAME SAL up_sal
---------- ---------- ----------
SMITH 800 801
JAMES 950 951
ADAMS 1100 1102
WARD 1250 1252
MARTIN 1250 1252
MILLER 1300 1302
TURNER 1500 1502
ALLEN 1600 1602
CLARK 2450 2453
BLAKE 2850 2853
JONES 2975 2978
SCOTT 3000 3003
FORD 3000 3003
KING 5000 5004

14 rows selected.

SQL>