Can try:

select ph.companyname,upper(ph.shortname)+replace(convert(varchar,convert(datetime,qm.quotation_date),1),'/','')+
convert(varchar,qm.seskey) as
[QuotationID],ph.seskey,
po.quotaion_id,
po.Purchage_No,
po.Purchage_Date,
po.Purchage_Amount,
po.Upload,po.Upload_Filename
from tbl_Partnerhirerege ph
join tbl_PurchaseOrder po on ph.seskey = po.userdid
join tbl_quotation q on ph.seskey = q.userdid
join tbl_quotation_master qm on ph.seskey = qm.userdid
where ph.seskey = 12 -- @company