left outer join 有关问题

left outer join 问题
select   Salesinvoices.SalesInvoiceID,SalesInvoiceItems.SalesInvoiceItemID,Salesinvoices.Companyid,Salesinvoices.Departmentid,Salesinvoices.Payer,Salesinvoices.Billdate,SalesinvoiceItems.Materialid,Salesinvoices.Employeeid,SaleQuantity,TaxInPrice,TaxInValue,TaxControlCode,
              0,0,0,0,Arapclearitems.*
from   SalesInvoiceItems
          inner   join   SalesInvoices   on   SalesInvoices.Salesinvoiceid=SalesInvoiceItems.Salesinvoiceid
          left   outer   join   ARAPClearItems
                          inner   join   ARAPClears   on   ARAPClears.Clearid   =ARAPClearItems.Clearid    
            on   nvl(ARAPClearItems.ARAPbillID, '   ')   =SalesInvoiceItems.Salesinvoiceid   and   nvl(ARAPClearItems.BillItemID, '   ')=SalesInvoiceItems.SalesinvoiceItemID   and   nvl(ARAPClearitems.Invsign, '   ')   =   '1 '
          where   companyid= '010101 '   and   substring(billdate,1,6)= '200703 '   and   payer= '00001964 '
为什么与
select   Salesinvoices.SalesInvoiceID,SalesInvoiceItems.SalesInvoiceItemID,Salesinvoices.Companyid,Salesinvoices.Departmentid,Salesinvoices.Payer,Salesinvoices.Billdate,SalesinvoiceItems.Materialid,Salesinvoices.Employeeid,SaleQuantity,TaxInPrice,TaxInValue,TaxControlCode,
              0,0,0,0,Arapclearitems.*
from   SalesInvoiceItems
          inner   join   SalesInvoices   on   SalesInvoices.Salesinvoiceid=SalesInvoiceItems.Salesinvoiceid
          left   outer   join   ARAPClearItems
                         
            on   nvl(ARAPClearItems.ARAPbillID, '   ')   =SalesInvoiceItems.Salesinvoiceid   and   nvl(ARAPClearItems.BillItemID, '   ')=SalesInvoiceItems.SalesinvoiceItemID   and   nvl(ARAPClearitems.Invsign, '   ')   =   '1 '
          where   companyid= '010101 '   and   substring(billdate,1,6)= '200703 '   and   payer= '00001964 '
执行结果不一样？下面的可以出来六条纪录。但是上面的没有纪录？就是因为left   outer   join没有匹配上吗？但是left   outer   join   不应该影响纪录的条数吧~

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太长，up
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太长，up
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太长，up
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左关联，右关联搞清楚，出了问题也没有大问题，仔细调试一下吧
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这也太长了吧
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上面的语句有问题:
inner join ARAPClears ON ARAPClears.Clearid =ARAPClearItems.Clearid

ON

nvl(ARAPClearItems.ARAPbillID, ' ') =SalesInvoiceItems.Salesinvoiceid and nvl

怎么又出来个on?
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好好看看内、外，左、右关联的区别吧.再看看SQL语句的优化问题.
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