I have 2 tables:

Table1:
docnumber
date
count
etc. etc.

Table2:
docnumber
priority

I need a update query that adds 'docnumber' from Table1 to Table2 if it don't exist in Table2.

try

INSERT INTO Table2 ( DocNumber )
SELECT Table1.DocNumber
FROM Table1 LEFT JOIN Table2 ON Table1.DocNumber = Table2.DocNumber
WHERE (((Table2.DocNumber) Is Null));

cant check it in MySQL, but it works ok in MS Access

Thank You!!!