Answer 1

It's an ambiguity error, mysql can't recognize which column you want to show. Most often it happens when there are two columns of the same name in two tables (the pain in the neck is an "id" column ;), like in the case of the JOIN statement.

To avoid that, try referencing the column by prefixing it with the table name, like:

SELECT table1.id, table2.id, name, city FROM table1 JOIN table2 on table1.id=table2.id