MySQL query: How to fix Error 1052 (ambiguous column)

Question

I keep getting an error when I run both of the following queries that the CUST_NUM is ambiguous. How can I fix this?

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>=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);

Answer 1

SELECT i.INV_NUM, i.CUST_NUM, i.CUST_LNAME, i.CUST_FNAME, i.INV_DATE, i.INV_AMOUNT FROM CH08_INVOICE i INNER JOIN CH08_CUSTOMER c1 ON (i.CUST_NUM = c1.CUST_NUM) WHERE i.CUST_BALANCE>=1000;

SELECT c1.CUST_LNAME, c1CUST_FNAME FROM CH08_CUSTOMER c1 JOIN CH08_CUSTOMER_2 c2 ON (c1.CUST_LNAME = c2.CUST_LNAME AND c1.CUST_FNAME = c2.CUST_FNAME);

Please check this query

Answer 2

Ambiguous column means the database don't know which table it must use the column.

Try using

SELECT  INV_NUM, i.CUST_NUM ...

or

SELECT  INV_NUM, c1.CUST_NUM ...

for explicity defining the table.