Oracle NVL函数不允许第二个参数作为datetime

Question

select nvl(trunc(null),trunc(sysdate)) from dual;

执行上述查询时,我收到以下错误

ORA-00932: inconsistent datatypes: expected NUMBER got DATE

看起来当我拿字符串或数字而不是trunc(sysdate)它运行正常.

Answer 1

从这里:

NVL的第一个参数是确定返回列的预期数据类型,trunc函数默认为NUMBER,因为它的参数为NULL.NVL的第二个参数需要匹配它没有的数据类型,因为它是一个日期.

SQL> select nvl(trunc(sysdate), sysdate) as mydate from dual;

MYDATE
-------------------
26/05/2006 00:00:00

SQL> select nvl(trunc(null), sysdate) as mydate from dual;
select nvl(trunc(null), sysdate) as mydate from dual
                        *
ERROR at line 1:
ORA-00932: inconsistent datatypes: expected NUMBER got DATE

或者你可以这样做:

SELECT NVL(TO_DATE(TRUNC(NULL)),SYSDATE) FROM dual;