求一条链表更新的sql语句

表Emp_Tracking
AccountNum SubAccount AccountType LastPackagePurchaseDate LastPackageExpireDate LastDateWithoutAmount LastDateWithAmount
----------- ----------- ----------- ----------------------- ----------------------- ----------------------- -----------------------
100 0 M 2011-12-01 00:00:00.000 2011-12-09 20:54:57.113 NULL NULL
100 1 M 2011-12-20 00:00:00.000 2011-12-09 20:54:57.113 NULL NULL
100 2 M 2011-10-07 00:00:00.000 2011-12-09 20:54:57.113 NULL NULL
100 3 M NULL 2011-12-09 20:54:57.113 NULL NULL
100 4 M NULL 2011-12-09 20:54:57.113 NULL NULL
100 5 M NULL 2011-12-09 20:54:57.113 NULL NULL
101 0 M 2011-12-03 00:00:00.000 2011-12-09 20:54:57.113 NULL NULL
101 1 M 2011-12-10 00:00:00.000 2011-12-09 20:54:57.113 NULL NULL
101 2 M 2011-12-03 00:00:00.000 2011-12-09 20:54:57.113 NULL NULL
101 3 M NULL 2011-12-09 20:54:57.113 NULL NULL

表Billing_SalesInvoice_Master
InvoiceId AccountNum SubAccount AccountType PurchaseDate InvoiceAmount
----------- ----------- ----------- ----------- ----------------------- ---------------------
1 100 0 M 2011-12-01 00:00:00.000 200.00
2 100 1 M 2011-12-01 00:00:00.000 400.00
3 100 1 M 2011-12-05 00:00:00.000 600.00
4 100 2 M 2011-10-07 00:00:00.000 100.00
5 101 0 M 2011-12-03 00:00:00.000 0.00
6 101 1 M 2011-12-10 00:00:00.000 0.00
7 101 1 M 2011-12-01 00:00:00.000 200.00
8 101 2 M 2011-12-03 00:00:00.000 0.00
9 101 2 M 2011-12-10 00:00:00.000 0.00
10 101 0 M 2011-12-15 00:00:00.000 0.00
11 100 2 M 2011-10-09 00:00:00.000 100.00

我要通过AccountNum,SubAccount,AccountType连接更新Emp_Tracking表中的字段LastPackageExpireDate 的值，
当在Emp_Tracking表中有而在表Billing_SalesInvoice_Master没有的话，则把LastPackageExpireDate值设置为Null,
如：100 - 3 - M这条记录的LastPackageExpireDate值设置为Null

SQL code

update
   a
set
   LastPackageExpireDate=b.LastPackageExpireDate
from
  Emp_Tracking a left join Billing_SalesInvoice_Master
on
  a.AccountNum=b.AccountNum and a.SubAccount=b.SubAccount and a.AccountType=b.AccountType

SQL code

update
   a
set
   LastPackageExpireDate=b.PurchaseDate
from
  Emp_Tracking a left join Billing_SalesInvoice_Master b
on
  a.AccountNum=b.AccountNum and a.SubAccount=b.SubAccount and a.AccountType=b.AccountType