The DECODE function is replaced by CASE expressions.
DECODE function expressions are quite difficult to read and it is not part of the ANSI/ISO SQL standard.
CASE expressions are much more powerful.
The following code shows a query where the DECODE function is used in the SELECT clause and in the ORDER BY clause.
SQL> SQL> drop table emp; Table dropped.-- w w w . j av a 2 s .co m SQL> create table emp( 2 empno NUMBER(4) primary key, 3 ename VARCHAR2(8) not null , 4 init VARCHAR2(5) not null , 5 job VARCHAR2(8) , 6 mgr NUMBER(4) , 7 bdate DATE not null , 8 msal NUMBER(6,2) not null , 9 comm NUMBER(6,2) , 10 deptno NUMBER(2) default 10) ; SQL> SQL> insert into emp values(7001,'SMITH','N', 'TRAINER', 7902,date '1975-12-17', 1800 , NULL, 20); SQL> insert into emp values(7002,'ALLEN','JAM','SALESREP',7006,date '1971-05-20', 1600, 300, 30); SQL> insert into emp values(7003,'WARD', 'TF' ,'SALESREP',7006,date '1972-03-02', 1250, 500, 10); SQL> insert into emp values(7004,'JACK', 'JM', 'MANAGER', 7009,date '1977-04-02', 2975, NULL, 20); SQL> insert into emp values(7005,'BROWN','P', 'SALESREP',7006,date '1976-09-28', 1250, 1400, 30); SQL> insert into emp values(7006,'BLAKE','R', 'MANAGER', 7009,date '1973-11-01', 2850, NULL, 10); SQL> insert into emp values(7007,'CLARK','AB', 'MANAGER', 7009,date '1975-06-09', 2450, NULL, 10); SQL> insert into emp values(7008,'SCOTT','DEF','TRAINER', 7004,date '1979-11-26', 3000, NULL, 20); SQL> insert into emp values(7009,'KING', 'CC', 'DIRECTOR',NULL,date '1972-10-17', 5000, NULL, 10); SQL> insert into emp values(7010,'BREAD','JJ', 'SALESREP',7006,date '1978-09-28', 1500, 0, 30); SQL> insert into emp values(7011,'ADAMS','AA', 'TRAINER', 7008,date '1976-12-30', 1100, NULL, 20); SQL> insert into emp values(7012,'JONES','R', 'ADMIN', 7006,date '1979-10-03', 8000, NULL, 30); SQL> insert into emp values(7902,'FORD', 'MG', 'TRAINER', 7004,date '1979-02-13', 3000, NULL, 20); SQL> insert into emp values(7934,'MARY', 'ABC','ADMIN', 7007,date '1972-01-23', 1300, NULL, 10); SQL> SQL> select job, ename 2 , decode(greatest(msal,2500) 3 ,2500,'cheap','expensive') as class 4 from emp 5 where bdate < date '1984-01-01' 6 order by decode(job,'DIRECTOR',1,'MANAGER',2,3); JOB | ENAME | CLASS -------- | -------- | --------- DIRECTOR | KING | expensive MANAGER | CLARK | cheap MANAGER | BLAKE | expensive MANAGER | JACK | expensive SALESREP | BROWN | cheap TRAINER | FORD | expensive ADMIN | MARY | cheap TRAINER | SCOTT | expensive SALESREP | ALLEN | cheap SALESREP | BREAD | cheap TRAINER | ADAMS | cheap JOB | ENAME | CLASS -------- | -------- | --------- ADMIN | JONES | expensive SALESREP | WARD | cheap TRAINER | SMITH | cheap 14 rows selected. SQL> SQL> --And then using CASE for the exact same result: SQL> SQL> select job, ename 2 , case greatest(msal,2500) 3 when 2500 then 'cheap' 4 else 'expensive' 5 end as class 6 from emp 7 where bdate < date '1984-01-01' 8 order by decode(job,'DIRECTOR',1,'MANAGER',2,3); JOB | ENAME | CLASS -------- | -------- | --------- DIRECTOR | KING | expensive MANAGER | CLARK | cheap MANAGER | BLAKE | expensive MANAGER | JACK | expensive SALESREP | BROWN | cheap TRAINER | FORD | expensive ADMIN | MARY | cheap TRAINER | SCOTT | expensive SALESREP | ALLEN | cheap SALESREP | BREAD | cheap TRAINER | ADAMS | cheap JOB | ENAME | CLASS -------- | -------- | --------- ADMIN | JONES | expensive SALESREP | WARD | cheap TRAINER | SMITH | cheap 14 rows selected. SQL>