1, 表T1中a列為timestamp類型,執(zhí)行sql:
select a from T1
union all
select null as a from T2;
報錯,修改方法如下:
select a from T1
union all
select cast(null as timestamp) as a from T2;
這樣就可以把null強制轉(zhuǎn)換成timestamp型, 同樣的還有:
CAST(NULL as CHAR)
CAST(NULL AS DATE)
CAST(NULL as INTEGER) ......
2, 在DB2中, 和Oracle中NVL函數(shù)功能相同的函數(shù)為 coalesce, 它的功能比oracle可能還要好一些(可以指定值, Oracle中nvl函數(shù)好像不可以這樣, 沒有仔細驗證) . 如: select coalesce(a,1) from T.