:: 极限 Linux ::Oracle HowTo:如何使用Oracle的Decode函数进行多值判断

Decode函数的语法结构如下:

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:

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.