title: MySQL query: How to fix Error 1052 (ambiguous column)
body: <p>I keep getting an error when I run both of the following queries that the CUST_NUM is ambiguous. How can I fix this?</p>
  
  <pre><code>SELECT  INV_NUM, CUST_NUM, CUST_LNAME, CUST_FNAME, INV_DATE, INV_AMOUNT
  FROM    CH08_INVOICE i 
  INNER JOIN CH08_CUSTOMER c1 ON (i.CUST_NUM = c1.CUST_NUM)
  WHERE   CUST_BALANCE&gt;=1000;
  
  
  SELECT CUST_LNAME, CUST_FNAME 
  FROM CH08_CUSTOMER c1 JOIN CH08_CUSTOMER_2 c2
  ON (c1.CUST_LNAME = c2.CUST_LNAME AND c1.CUST_FNAME = c2.CUST_FNAME);
  </code></pre>