Oracle DB 嵌套函数
单行函数可以嵌套到任意深度。嵌套函数的计算顺序是从最内层到最外层。下面的一些示例显示这类函数的灵活性。
示例显示部门60 中的雇员的姓氏。该SQL 语句的计算涉及以下三个步骤：
1.内部函数检索姓氏的前8 个字符。
Result1 = SUBSTR (LAST_NAME, 1, 8)
2.外层函数将结果与_US连接在一起。
Result2 = CONCAT(Result1, '_US')
3.最外层函数将结果转换为大写。
因为没有给出列别名，所以整个表达式就成为列标题。
示例：
显示距聘用日期六个月后的下一个星期五的日期。按聘用日期对结果排列。
Next 6 Month Review
-------------------------------------------------------------------------------------
Friday, July 20th, 2001
Friday, December 13th, 2002
Friday, December 13th, 2002
，
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