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如何使用oracle的decode函数进行多值判断

作者：黑客防线网安Oracle维护基地来源：黑客防线网安Oracle维护基地浏览次数：0

黑客防线网安网讯：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, res...

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
DBSNMP                         SYSTEM
SCOTT                          SYSTEM
OUTLN                          SYSTEM                         2007-7-30 1
WMSYS                          SYSTEM                         2007-7-30 1
ORDSYS                         SYSTEM                         2007-7-30 1
ORDPLUGINS                     SYSTEM                         2007-7-30 1
MDSYS                          SYSTEM                         2007-7-30 1
CTXSYS                         DRSYS                          2007-7-30 1
XDB                            XDB                            2007-7-30 1
ANONYMOUS                      XDB                            2007-7-30 1
WKSYS                          DRSYS                          2007-7-30 1
WKPROXY                        DRSYS                          2007-7-30 1
ODM                            ODM                            2007-7-30 1
ODM_MTR                        ODM                            2007-7-30 1
OLAPSYS                        CWMLITE                        2007-7-30 1
RMAN                           TOOLS                          2007-7-30 1
HR                             EXAMPLE                        2007-7-30 1
OE                             EXAMPLE                        2007-7-30 1

USERNAME                       DEFAULT_TABLESPACE             LOCK_DATE
------------------------------ ------------------------------ -----------
PM                             EXAMPLE                        2007-7-30 1
SH                             EXAMPLE                        2007-7-30 1
QS_ADM                         EXAMPLE                        2007-7-30 1
QS                             EXAMPLE                        2007-7-30 1
QS_WS                          EXAMPLE                        2007-7-30 1
QS_ES                          EXAMPLE                        2007-7-30 1
QS_OS                          EXAMPLE                        2007-7-30 1
QS_CBADM                       EXAMPLE                        2007-7-30 1
QS_CB                          EXAMPLE                        2007-7-30 1
QS_CS                          EXAMPLE                        2007-7-30 1

30 rows selected

SQL> select username,decode(lock_date,null,'unlocked') status from t;

USERNAME                       STATUS
------------------------------ --------
SYS                            unlocked
SYSTEM                         unlocked
DBSNMP                         unlocked
SCOTT                          unlocked
OUTLN
WMSYS
ORDSYS
ORDPLUGINS
MDSYS
CTXSYS
XDB
ANONYMOUS
WKSYS
WKPROXY
ODM
ODM_MTR
OLAPSYS
RMAN
HR
OE