oracleI基础入门函数decode Crazy

 decode()函数

DECODE函数是ORACLE PL/SQL功能强大的函数之一。

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。
举例:
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.