Oracle decode

语法结构如下：
decode (expression, sch_1, res_1)
decode (expression, sch_1, res_1, sch_2, res_2)
decode (expression, sch_1, res_1, sch_2, res_2, ...., sch_n, res_n)
decode (expression, sch_1, res_1, default)
decode (expression, sch_1, res_1, sch_2, res_2, default)
decode (expression, sch_1, res_1, sch_2, res_2, ...., sch_n, res_n, default)
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。

Oracle decode

原文：http://blog.51cto.com/2012ivan/2064919