photo_x is not null or photo_x''的问题为什么photo_x is not null 和 photo_x''要都用上呢?这两句不是都在判断photo_x是不是非空吗?有什么用处?

photo_x is not null or photo_x''的问题为什么photo_x is not null 和 photo_x''要都用上呢?这两句不是都在判断photo_x是不是非空吗?有什么用处? Is Not Null 是什么 SQL中IS NOT NULL与!=NULL是等价的吗同题 数据库中语句is not null和!=null有什么区别? the specified call count is not a number:null payment_no is not allow null 给翻译下 (not studentr.date is null),SQLsql中有这种写法吗？not 字段 is null 这是什么意思？？？？ GROUP BY ROLLUP (A,B,C) HAVING A IS NOT NULL AND D NOT NULL是什么意思啊 哪位高手知道? COLLATE Chinese_PRC_CI_AS NOT NULL SQL中,下列空操作不正确的是 A.AGE IS NULL B.AGE IS NOT NULL C.AGE = NULL D.NOT (AGE IS NULL)说说它为什么错吧 GROUP BY ROLLUP (A,B,C) HAVING A IS NOT NULL AND D NOT Name must not be null OBJECT_ID ('student',在SQL里IF OBJECT_ID ('student','U') IS NOT NULL U payment_no is not allow null 信用卡支付失败.弹出来的 数据库中if OBJECT_ID ('dbo.table_test_6_1','u') is not null drop table table_test_6_1判断是否存在该 这句sql是什么意思,能不能逐字解释啊if db_id(N'test') is not null drop database test go /null was not found on this server. SQL 请高手帮忙看一下以下语法哪里有错误.USE tempdb;IF OBJECT_ID('dbo.Arrays') IS NOT NULL DROP TABLE dbo.Arrays;CREATE TABLE dbo.Arrays(arrid VARCHAR(10) NOT NULL PRIMARY KEY,array VARCHAR(8000) NOT NULL)GOINSERT INTO Arrays(arrid,arr