Warning: Null value is eliminated by an aggregate or other SET operation.

Null 值會被聚合函數忽略，默認情況下，Sql Server會給出Warning：

Warning: Null value is eliminated by an aggregate or other SET operation.

這個Warning說明Null value 被聚合函數忽略，此時的 SET ANSI_WARNINGS 選項是ON狀態，例如，count()函數不會計算null值，min/max函數不會計算null值。如果設置 SET ANSI_WARNINGS OFF ，SQL Server不會拋出 warning 消息。

1，忽略NULL 值

例如，結果是1，正確，但是出現一個Warning。

use tempdb
go 

set ANSI_WARNINGS on 

if object_id('#dt_test','U') is not null
    drop table #dt_test

create table #dt_test
(    
    id int
)

insert into #dt_test
values(1),(null)

select min(id)
from #dt_test

強烈推薦：將ANSI_Warnings選項設置為ON

2，查看當前DB的 ANSI_Warnings 選項的設置

select name,
    database_id,
    is_ansi_warnings_on
from sys.databases
where database_id=db_id()

 

引用《SET ANSI_WARNINGS》：

As the Warning says, NULLs are being ignored because we are using aggregate function (SUM, AVG). To avoid the warning we can use “set ansi_warnings off” before the script. Here is the modified script.

SET ANSI_WARNINGS OFF

When set to ON, if null values appear in aggregate functions, such as SUM, AVG, MAX, MIN, STDEV, STDEVP, VAR, VARP, or COUNT, a warning message is generated. When set to OFF, no warning is issued. 

SET ANSI_WARNINGS must be ON when you are creating or manipulating indexes on computed columns or indexed views. If SET ANSI_WARNINGS is OFF, CREATE, UPDATE, INSERT, and DELETE statements on tables with indexes on computed columns or indexed views will fail

 

參照文檔：

SET ANSI_WARNINGS (Transact-SQL)