Hi @derek chan
the output is "no rows select"
That's because the id column of Table 2 doesn't have data that matches the documentid column of Table 1, so 'no rows select'.
As shown in this image:
If you want the customerid in Table 1 to always be displayed,then you could try Table1 LEFT JOIN Table2
Refer to this doc for more information.
Best regards,
LiHong