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  • 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.
     

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  • 原文地址:https://www.cnblogs.com/flyscan/p/2513454.html
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