1:使用decode判断字符串是否一样

DECODE(value,if1,then1,if2,then2,if3,then3,...,else)

含义为

IF 条件=值1 THEN

RETURN(value 1)

ELSIF 条件=值2 THEN

RETURN(value 2)

......

ELSIF 条件=值n THEN

RETURN(value 3)

ELSE

RETURN(default)

END IF

select empno,

decode(empno,7369,'smith',7499,'allen',7521,'ward',7566,'jones','unknow')

as name from emp where rownum<=10

2:使用decode比较大小

select decode(sign(var1-var2),-1,var1,var2) from dual

sign()函数根据某个值是0、正数还是负数，分别返回0、1、-1

select decode(sign(100-90),-1,100,90) from dual