Decode函数的语法结构如下:

复制代码 代码如下:

decode (expression, search_1, result_1)

decode (expression, search_1, result_1, search_2, result_2)

decode (expression, search_1, result_1, search_2, result_2, ...., search_n, result_n)

decode (expression, search_1, result_1, default)

decode (expression, search_1, result_1, search_2, result_2, default)

decode (expression, search_1, result_1, search_2, result_2, ...., search_n, result_n, default)

decode函数比较表达式和搜索字，如果匹配，返回结果；如果不匹配，返回default值；如果未定义default值，则返回空值。

以下是一个简单测试，用于说明Decode函数的用法:

复制代码 代码如下:

SQL> create table t as select username,default_tablespace,lock_date from dba_users;

Table created.

SQL> select * from t;

USERNAME DEFAULT_TABLESPACE LOCK_DATE

------------------------------ ------------------------------ ---------

SYS SYSTEM

SYSTEM SYSTEM

OUTLN SYSTEM

CSMIG SYSTEM

SCOTT SYSTEM

EYGLE USERS

DBSNMP SYSTEM

WMSYS SYSTEM 20-OCT-04

8 rows selected.

SQL> select username,decode(lock_date,null,"unlocked","locked") status from t;

USERNAME STATUS

------------------------------ --------

SYS unlocked

SYSTEM unlocked

OUTLN unlocked

CSMIG unlocked

SCOTT unlocked

EYGLE unlocked

DBSNMP unlocked

WMSYS locked

8 rows selected.

SQL> select username,decode(lock_date,null,"unlocked") status from t;

USERNAME STATUS

------------------------------ --------

SYS unlocked

SYSTEM unlocked

OUTLN unlocked

CSMIG unlocked

SCOTT unlocked

EYGLE unlocked

DBSNMP unlocked

WMSYS

8 rows selected.