Oracle 中 decode 函数用法

含义解释：decode(条件,值1,返回值1,值2,返回值2,...值n,返回值n,默认值)该函数的含义如下：IF 条件=值1 THEN　　　　RETURN(翻译值1)ELSIF 条件=值2 THEN　　　　RETURN(翻译值2)　　　　......ELSIF 条件=值n THEN　　　　RETURN(翻译值n)ELSE　　　　RETURN(缺省值)END IFdecode(字段或字段的运算，值1，值2，值3）       这个函数运行的结果是，当字段或字段的运算的值等于值1时，该函数返回值2，否则返回值3当然值1，值2，值3也可以是表达式，这个函数使得某些sql语句简单了许多create table table_subject(   "id" int primary key not null,   subject_name varchar2(20)  not null，   score int not null)create sequence subject_seq ;insert into table_subject values(subject_seq.nextval,'语文',98);insert into table_subject values(subject_seq.nextval,'英语',67);insert into table_subject values(subject_seq.nextval,'数学',90);insert into table_subject values(subject_seq.nextval,'数学',89);insert into table_subject values(subject_seq.nextval,'语文',97);insert into table_subject values(subject_seq.nextval,'语文',96);insert into table_subject values(subject_seq.nextval,'语文',95);insert into table_subject values(subject_seq.nextval,'英语',78);select * from table_subject group by subject_name;--按照中文指定字段排序(语文、数学、英语)--其中1，2,3 代表显示的顺序select * from table_subject order by decode(subject_name, '语文', 1, '数学', 2 ,'英语',3);

select * from table_subject order by decode(subject_name, '语文', 3, '数学', 2 ,'英语',1);-- 一条语句统计语数英的数量select   sum(decode(subject_name,'语文'，1，0)) as "语文"，  sum(decode(subject_name,'数学'，1，0)) as "数学",  sum(decode(subject_name,'英语'，1，0)) as "英语" from table_subject;