decode [Oracle SQL]-优快云博客

本文详细介绍了 Oracle SQL 中的 DECODE 函数用法，包括不同参数组合下的使用方式及返回值规则，并通过示例展示了如何利用该函数进行条件判断。

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原文：[url]http://www.adp-gmbh.ch/ora/sql/decode.html[/url]

参考：[url]http://www.psoug.org/reference/decode_case.html[/url]
[url]http://techonthenet.com/oracle/functions/decode.php[/url]
[code]decode [Oracle SQL]

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 compares expression to the search_x expressions and, if matches, returns result_x. If not, returns default, or, if default is left out, null.
This is demonstrated with the following example:

create table a (x int, b int);

insert into a values (1,2);
insert into a values (1,3);
insert into a values (2,4);
insert into a values (2,5);
insert into a values (3,6);

select * from a where b = decode (x,1,2,2,4);

X B
---------- ----------
1 2
2 4[/code]

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