使用Oracle的Decode函數進行多值判斷

更新時間：2013年05月04日 23:43:46 作者：

decode函數比較表達式和搜索字，如果匹配，返回結果；如果不匹配，返回default值；如果未定義default值，則返回空值

Decode函數的語法結構如下:

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函數比較表達式和搜索字，如果匹配，返回結果；如果不匹配，返回default值；如果未定義default值，則返回空值。
以下是一個簡單測試，用于說明Decode函數的用法:

復制代碼代碼如下:

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.

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