ANSI_NULLS 和 CONCAT_NULL_YIELDS_NULL

在sqlserver宝典上又看到了这两个属性，研究了一下。

 

declare @tb table(s varchar(50)) insert into @tb select null insert into @tb select null insert into @tb select 'Edwin' set ansi_nulls off select count(*) from @tb where s=null select count(*) from @tb where s<>null select count(*) from @tb where s is null select count(*) from @tb where s is not null set ansi_nulls on select count(*) from @tb where s=null select count(*) from @tb where s<>null select count(*) from @tb where s is null select count(*) from @tb where s is not null set concat_null_yields_null on select s+'1' from @tb select ISNULL(s,'')+'1' from @tb set concat_null_yields_null off select s+'1' from @tb select ISNULL(s,'')+'1' from @tb 

最后的查询都是推荐方案。不建议使用属性设置的方式！

sql-92 标准要求对空值的等于 (=) 或不等于 (<>) 比较取值为 FALSE。当set ansi_nulls on时，就符合了92标准。