同样的sql在mybatis查询和mysql查询结果不同，求解。

Question

mapper中代码

select
			AA.fileID,
			AA.file_address,
			AA.uploader,
			AA.upload_time,
			AA.parent_module,
			AA.submodule,
			AA.file_name
		from (
			select if (@pa=f.fileID,@rank:=@rank+1,@rank:=1) rank,
				@pa:=f.fileID as fileID,
				f.file_address,
				f.uploader,
				f.upload_time,
				f.parent_module,
				f.submodule,
				f.file_name
			 from (
				select
					fileID,
					file_address,
					uploader,
					upload_time,
					parent_module,
					submodule,
					file_name
				from files 
					<where>
						<if test="parent_module != '' and parent_module != null">parent_module = #{parent_module}</if>
						<if test="fileID != '' and fileID != null ">AND fileID = #{fileID}</if>
						<if test="submodule != '' and submodule != null ">AND submodule = #{submodule}</if>
					</where>  
					order by fileID asc, upload_time desc
				) f,
				(select @rank:=0,@pa='') tt
			) AA
			where AA.rank=1
		order by AA.fileID

mysql中代码

select
			AA.ID,
			AA.fileID,
			AA.file_address,
			AA.uploader,
			AA.upload_time,
			AA.parent_module,
			AA.submodule,
			AA.file_name,
			AA.ps_log_id,
			AA.blueprint_category
		from (
			select if (@pa=f.fileID,@rank:=@rank+1,@rank:=1) rank,
				@pa:=f.fileID as fileID,
				f.ID,
				f.file_address,
				f.uploader,
				f.upload_time,
				f.parent_module,
				f.submodule,
				f.file_name,
				f.ps_log_id,
				f.blueprint_category
			 from (
				select
					ID,
					fileID,
					file_address,
					uploader,
					upload_time,
					parent_module,
					submodule,
					file_name,
					ps_log_id,
					blueprint_category
				from files 
					WHERE parent_module = '产品中心'
					AND submodule='外部文档'
					AND fileID='PJ002'
					order by fileID asc, upload_time desc
				) f,
				(select @rank:=0,@pa='') tt
			) AA
			where AA.rank=1
		order by AA.fileID

然后前者不能实现按fileID分组后取第一个，后者能实现分组取第一个，别问我为啥不用group by，服务器的mysql的sql_mode属性值无法去掉only_full_group_by，怎么修改配置文件都没用，只能写这么麻烦的sql，但转换到mapper文件里效果就不行了

Answer 1

追加，我打印出来的mybatis的的代码和sql的是一样的处理入参的值为?

select 
AA.fileID, 
AA.file_address, 
AA.uploader, 
AA.upload_time, 
AA.parent_module, 
AA.submodule, 
AA.file_name 
from ( 
select if (@pa=f.fileID,@rank:=@rank+1,@rank:=1) rank, 
@pa:=f.fileID as fileID, 
f.file_address, 
f.uploader, 
f.upload_time, 
f.parent_module, 
f.submodule, 
f.file_name 
from ( 
select fileID, 
file_address, 
uploader, 
upload_time, 
parent_module, 
submodule, 
file_name 
from files 
WHERE parent_module = ? 
AND fileID = ? 
AND submodule = ?
order by 
fileID asc, 
upload_time desc 
) f, 
(select @rank:=0,@pa='') tt 
) 
AA where AA.rank=1 
order by AA.fileID 

且，我在mysql中测试时发现，新建查询时，第一次执行，所以的rank列的值都是1，第二次执行时就能正确编号，怀疑第一次执行时

select if (@pa=f.fileID,@rank:=@rank+1,@rank:=1) rank,

这句代码的if判定结果都是走的false，但为啥会这样就没想明白，求大佬解惑