ms access 2000：DSum 的参数太少

Question

I have this problem for like an hour now and I just can't find the solution through Google, so maybe someone here can help me? I have this table here:

|--------------------------|
|          Table1          |
| Product | Amount | Buyer |
|--------------------------|
|    Food |      4 |     1 |
|   Paper |     30 |     1 |
|    Food |      2 |     2 |
|--------------------------|

And I want to have this table here:

|-------------------|
|       table2      |
| Buyer | Purchases |
|-------------------|
|     1 |        34 |
|     2 |         2 |
|-------------------|

Before the code is executed, table2 looks like this:

|-------------------|
|       table2      |
| Buyer | Purchases |
|-------------------|
|     1 |           |
|     2 |           |
|-------------------|

The code I tried is:

UPDATE table2
SET Purchases = (
  DSum("Amount", "table1", "table1.Buyer = " & table2.Buyer)
)

However, I get the following error:

Too few parameters. Expected 1

If I remove the last part of the DSum method:

UPDATE table2
SET Purchases = (
  DSum("Amount", "table1")
)

I don't get an error. What did I do wrong?

Answer 1

Don't include the table names:

UPDATE 
    table2
SET 
    Purchases = DSum("Amount", "table1", "Buyer = " & Buyer & "")

No single quotes as Buyer is a number.