update table based on another tables value in sqLite

We have two tables table1 table2

In table1

Itemnumber    SalesCode
123            213UB
142            132NB
1458           256GD

In table2
Itemnumber    ProductGroupCode
123            
142           
1458  

After Update table2 We need Like this

 Itemnumber    ProductGroupCode
    123            213UB
    142            132NB
    1458           256GD

We tried like this

tx.executeSql('UPDATE  table2 JOIN  table1 ON (table2.ItemNumber=table1.ItemNumber) SET table2.CustomerPriceGroup = table1.SalesCode');

But We got error like this

Colud not prepare Statement (Near "JOIN ":syntax error)

Please tell me what wrong in my code