我有以下的 select 语句，它几乎瞬间完成。
declare @weekending varchar(6)
set @weekending = 100103
select InvoicesCharges.orderaccnumber, Accountnumbersorders.accountnumber
from Accountnumbersorders, storeinformation, routeselecttable,InvoicesCharges, invoice
where InvoicesCharges.pubid = Accountnumbersorders.publication
and Accountnumbersorders.actype = 0
and Accountnumbersorders.valuezone = 'none'
and storeinformation.storeroutename = routeselecttable.istoreroutenumber
and storeinformation.storenumber = invoice.store_number
and InvoicesCharges.invoice_number = invoice.invoice_number
and convert(varchar(6),Invoice.bill_to,12) = @weekending
然而，等效的更新语句需要1分40秒。
declare @weekending varchar(6)
set @weekending = 100103
update InvoicesCharges
set InvoicesCharges.orderaccnumber = Accountnumbersorders.accountnumber
from Accountnumbersorders, storeinformation, routeselecttable,InvoicesCharges, invoice
where InvoicesCharges.pubid = Accountnumbersorders.publication
and Accountnumbersorders.actype = 0
and dbo.Accountnumbersorders.valuezone = 'none'
and storeinformation.storeroutename = routeselecttable.istoreroutenumber
and storeinformation.storenumber = invoice.store_number
and InvoicesCharges.invoice_number = invoice.invoice_number
and convert(varchar(6),Invoice.bill_to,12) = @weekending
即使我添加了：
and InvoicesCharges.orderaccnumber <> Accountnumbersorders.accountnumber
在更新语句的末尾将写入数量减少到零后，所需时间相同。
我这里有什么做错了吗？为什么会有如此巨大的差异？