Oracle-函数Decode进行多值判断

最新推荐文章于 2023-10-28 17:24:40 发布

转载最新推荐文章于 2023-10-28 17:24:40 发布 · 1.8k 阅读

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原文链接：http://www.cnblogs.com/hwaggLee/p/5335967.html

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#数据库

Oracle数据库中的Decode函数用于进行多值判断，当给定的表达式与搜索字匹配时，返回相应结果，否则返回默认值或空值。其语法结构包括比较表达式、搜索字和返回结果。本文通过一个简单的测试案例，展示了Decode函数的基本用法。

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

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.