select
    a.order_line,
    a.product_id,
    a.sales,
    b.customer_name,
    b.age
from sales_2015 as a
inner join customer_20_60 as b
   on a.customer_id = b.customer_id 
order by customer_id;

I got an error message: column reference "customer_id is ambiguous. How do I solve this problem?

CodePudding user response：

Just means that multiple tables have same column name and it doesn't know which to use.

In your case, both - sales_2015 and customer_20_60 tables have the column customer_id.

Make sure you use the a.customer_id or b.customer_id in all the places. Based on the code you have pasted, looks like the only place this is missing is in the order by clause.