char 列名 无效
declare @letter char(1)
declare @sql varchar(299)

set @letter= 'a '

set @sql= 'select * from syinfo_subzone '
set @sql=@sql+ ' where sz_letter =cast(@letter as char(1)) '
exec (@sql)

服务器: 消息 207，级别 16，状态 3，行 1
列名 'a ' 无效。

[解决办法]
declare @letter char(1)
declare @sql varchar(299)

set @letter= 'a '

set @sql= 'select * from syinfo_subzone '
set @sql=@sql+ ' where sz_letter = ' ' ' +cast(@letter as char(1)) + ' ' ' '
exec (@sql)
[解决办法]
--try

declare @letter char(1)
declare @sql varchar(299)

set @letter= 'a '

set @sql= 'select * from syinfo_subzone '
set @sql=@sql+ ' where sz_letter =cast( '+@letter+ ' as char(1)) '
exec (@sql)
[解决办法]
--试试
declare @sql varchar(299)
set @sql= 'declare @letter char(1) set @letter= ' 'a ' ' select * from syinfo_subzone where sz_letter =cast(@letter as char(1)) '
exec (@sql)


[解决办法]
这样看看:
declare @letter char(1)
declare @sql varchar(299)

set @letter= 'a '

set @sql= 'select * from syinfo_subzone '
set @sql=@sql+ ' where sz_letter = '+@letter
exec (@sql)