SqlServer_查询带有null的记录
字段的三种不同状态
select distinct status from t_table
(NULL)
XXX
YYY不同状态的记录数
select count(1) from t_table 35709
select count(1) from t_table where status = 'XXX' 17579 XXX
select count(1) from t_table where status = 'YYY' 4242 YYY
select count(1) from t_table where status is null 13888 (NULL)
select count(1) from t_table where status = null 0
select count(1) from t_table where status is not null 21821 XXX+ YYY
select count(1) from t_table where status <> null 0
select count(1) from t_table where status != null 0 1
select count(1) from t_table where status != 'XXX' 4242 不含null值记录
select count(1) from t_table where status != 'YYY' 17579 不含null值记录
select count(1) from t_table where status != 'XXX' and status != 'YYY' 0 != 不包含 null值的记录2
select count(1) from t_table where status in (select status from t_table) 21821
select count(1) from t_table where status in (select status from t_table where status = 'XXX' ) 17579
select count(1) from t_table where status in (select status from t_table where status = 'YYY' ) 4242
select count(1) from t_table where status in (select status from t_table where status in ('XXX','YYY') ) 218213
select count(1) from t_table where status in ('XXX' ) 17579
select status from t_table where status not in ('XXX' ) 4242 not in 是不包含 (默认null值)的记录
select count(1) from t_table where status not in ('') 21821
select count(1) from t_table where status not in (null) 0 not in (null) 返回空 ANSISQL（SQL-92）规定
select count(1) from t_table where status in (null) 0 in (NULL) 返回空 ANSISQL（SQL-92）规定
select count(1) from t_table where status is null 13888 查询 带有null值得记录 最好不要使用 in
select count(1) from t_table where status is not null 21821 使用了 in 是 不查询 null 的记录的4
select status from t_table where status not in ('XXX','YYY') (默认null值) 返回空结果集
select region,isNull(region,'11') from t_table where status not in ('XXX','YYY') (默认null值) 加了where 后面的条件查询不到记录 ,返回空结果集,region都没有,也不会进行null判断
select COALESCE(region,'11') from t_table where status not in ('XXX','YYY') (默认null值) 返回空结果集5
select count(1) from t_table where status not in (select status from t_table ) 0
select isNull(region,'22') from t_table where status not in ('XXX','YYY') 显示(Null),其实是 返回的 空结果集
select count(1) from t_table where status not in ('XXX','YYY') 0
select count(1) from t_table where status not in (select status from t_table where status not in ('XXX','YYY') ) 35709 not in (空结果集) 所以,能查出所有数据
select count(1) from t_table where status in ( null) 0 in (NULL) ANSISQL（SQL-92）规定的Null值的比较取值结果都为False，既Null=Null取值也是False
select count(1) from t_table where status not in ( null) 0 not in (NULL) ANSISQL（SQL-92）规定的Null值的比较取值结果都为False，既Null=Null取值也是False
select count(1) from t_table where status in (select status from t_table where status not in ('XXX','YYY') ) 0 in (默认null值)
select count(1) from t_table where status <> (select status from t_table where status not in ('XXX','YYY') ) 0 <> (默认null值)
select count(1) from t_table where status != (select status from t_table where status not in ('XXX','YYY') ) 0 != (默认null值)
select count(1) from t_table where status != null 0 ANSISQL（SQL-92）规定
select count(1) from t_table where status <> null 0 ANSISQL（SQL-92）规定默认情况下，推荐使用 IS NOT NULL去判断，因为SQL默认情况下对！= Null的判断会永远返回0行，但没有语法错误。
如果你一定想要使用！= Null来判断，需要加上这个语句：
set ANSI_NULLS off所以我们要牢记：默认情况下做比较条件时使用关键字“is null”和“is not null”。
如果你一定要使用!= null来进行条件判断，需要加上这个命令语句：SET ANSI_NULLS OFF，这时数据库进入ANSI SQL非标准模式，你会发现IS NOT NULL 和 != null 是等效的了。
这里使用的是模式切换命令SET ANSI_NULLS[ON/OFF]。ON值采用ANSI SQL严格标准，OFF值采用非标准兼容模式。另外SET ANSI_DEFAULTS [ON/OFF]命令也可以实现标准的切换，只是这个命令控制的是一组符合SQL-92标准的设置，其中就包括Null值的标准。
默认情况下，数据库管理程序（DB-Library）是SET ANSI_NULLS为OFF的。但是我们的大多数应用程序，都是通过ODBC或者OLEDB来访问数据库的，作为一种开放兼容的数据库访问程序，或许是兼容性的考虑，SETANSI_NULLS值设置为ON。这样一来带来的一些问题是需要注意的。像存储过程或者自定义函数这样的应用程序都是基于DB-Library的，默认情况下，SETANSI_NULLS为OFF，并且在这样的程序中，不能使用SETANSI_NULLS在一个环境中修改规则，只能修改数据库配置参数。
执行 set ANSI_NULLS off 后
select count(1) from t_table where status in ( null) 13888
select count(1) from t_table where status not in ( null) 21821
select count(1) from t_table where status in (select status from t_table where status not in ('XXX','YYY') ) 13888
select count(1) from t_table where status <> null 21821
select count(1) from t_table where status <> (select status from t_table where status not in ('XXX','YYY') )
select status from t_table where status not in ('XXX','YYY') 返回 13888 条 null值记录 导致下面的报错
[Err] 21000 - [SQL Server]Subquery returned more than 1 value.
This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression.
set ANSI_NULLS on 时 ,下面sql 返回的是 null ,不会出现语法报错的情况
select status from t_table where status not in ('XXX','YYY')
select count(1) from t_table where status != (select status from t_table where status not in ('XXX','YYY') ) 语法报错 slq_不使用or查询 0 和null_ISNULL(a.status ,0)=0 和 case when else end
SQL中IS NOT NULL与!=NULL的区别