UPDATE statement with INNER JOIN

Hi,

I encountered an error when trying to use a UPDATE statement with INNER JOIN.

First let me explain to you the task I have. I have two tables tbl_A and tbl_B like this:

                   tbl_A                                                      tlb_B
caseID   fld_a    fld_b                 caseID    fld_1   fld_2   fld_3
    1          aaa     bbb                       2         ddd     eee     fff
    2           dd       ee                        4         ggg     hhh      iii

I want to INSERT values of caseID, fld_1 and fld_2 from tbl_B into fld_a and fld_b of tbl_A for those caseIDs that tbl_A does not have. However, I want to UPDATE records in tbl_A with values from tbl_B for those caseID that also in tbl_B. So, the result should look like this:

                   tbl_A                                                  
caseID   fld_a    fld_b                
    1          aaa     bbb                
    2          ddd     eee                    
    4          ggg     hhh

Note here caseID in tbl_A is the primary key. No duplicates are allowed.

I can use INSERT INTO statement to insert records. It works fine. But when I tried the following UPDATE statement with INNER JOIN, error occurs.

UPDATE tbl_A SET tbl_A.fld_a = tbl_B.fld_1, tbl_A.fld_b = tbl_B.fld_2 FROM tlb_A INNER JOIN tbl_B ON tbl_A.caseID = tbl_B.caseID

Can anyone tell me where goes wrong? Or do you have any better way to achieve the task that I mentioned?

Thank you very much.