ExecuteSQL could be used for this, but it's not really needed.
Define this relationship in Manage | Database | Relationship:
Table 1::Week = Table 2::Week AND
Table 1::Day = Table 2: Day
Then you can place the Sales field from Table 2 on your table 1 layout to show the sales once you enter a week and day in the current record of table 1 that matches to a record in Table 2. If you need to physically copy this data (don't do this unless you have a specific reason), you can use auto-enter field options on a field in Table 1 using either the looked up value option or a calculation to copy over the sales value from the matching record.