如何避免万一表达多功能执行不筑巢

Question

因此，让我们假设我有以下查询：

SELECT 
    CASE 
    WHEN SOME_PACKAGE.SOME_EXPENSIVE_FUNCTION IS NOT NULL 
    THEN SOME_PACKAGE.SOME_EXPENSIVE_FUNCTION || ', random string' 
    ELSE 
    'something_else' 
    END 
FROM 
    SOME_TABLE; 

是否有办法防止这种封装功能从没有嵌套查询执行不止一次？

Answer 1

这应该工作：

SELECT NVL(NULLIF(SOME_PACKAGE.SOME_EXPENSIVE_FUNCTION 
    ||', random string',', random string'),'something_else') 
FROM SOME_TABLE;