Select 添加字段时出现语法错误

下面的代码对于求平均值很有效

 select
 [state], areatype, area, '00' [period], indcode, ownership, 
 avg(sites) sites, avg(employment) employment
 from dbo.tablename
 group by [state], areatype, area, indcode, ownership;

我保持它的简短和简单，以便学习这个概念。我在第二行和第五行添加了两个字段，现在出现语法错误。有什么见解吗

 select
 [state], areatype, area, periodyear, '00' [period], indcodetype, indcode, ownership, 
 avg(sites) sites, avg(employment) employment
 from dbo.tablename
 group by [state], areatype, area, periodyear, incodetype, indcode, ownership;

Msg 102, Level 15, State 1, Line 2
Incorrect syntax near 'sites'.

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由于我无法解释的原因，我一次只添加一个元素，它正在工作。如果我全部输入，我会得到语法错误，但是如果我从有效的开始，一次添加一个项目并执行，它就有效了

请分享你得到的错误