使用Oracle的Decode函数进行多值判断建站知识
导读:1
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企业网站建设, 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 SYSTEMSYSTEM SYSTEMOUTLN SYSTEMCSMIG SYSTEMSCOTT SYSTEMEYGLE USERSDBSNMP SYSTEMWMSYS SYSTEM 20-OCT-04
8 rows selected.
SQL> select username,decode(lock_date,null,"unlocked","locked") status from t;
USERNAME STATUS------------------------------ --------SYS unl网站建设教程ockedSYSTEM unlockedOUTLN unlockedCSMIG unlockedSCOTT unlockedEYGLE unlockedDBSNMP unlockedWMSYS locked
8 rows selected.
SQL> select username,decode(lock_date,null,"unlocked") status from t;
USERNAME STATUS------------------------------ --------SYS unlockedSYSTEM unlockedOUTLN unlockedCSMIG unlockedSCOTT unlockedEYGLE unlockedDBSNMP unlockedWMSYS
8 rows selected.
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