PHP - Deleting duplicate values with same ref - php

Question

I've the following MySQL Table called store
id ref item_no supplier
1 10 x1 usa
2 10 x1 usa
3 11 x1 china
4 12 x2 uk
5 12 x3 uk
6 13 x3 uk
7 13 x3 uk
Now What i'm excepting the output to be is as follows :
id ref item_no supplier
1 10 x1 usa
3 11 x1 china
4 12 x2 uk
5 12 x3 uk
6 13 x3 uk
As you can see item_no x1 and x3 have same ref and supplier source, so what I want is to delete the duplicate record in-order to keep one item_no only !
I've create this PHP code to SELECT results only :
$query1 = "SELECT
DISTINCT(item_no) AS field,
COUNT(item_no) AS fieldCount,
COUNT(ref) AS refcount
FROM
store
GROUP BY item_no HAVING fieldCount > 1";
$result1 = mysql_query($query1);
if(mysql_num_rows($result1)>0){
while ($row1=mysql_fetch_assoc($result1)) {
echo $row1['field']."<br /><br />";
}
} else {
//IGNORE
}
How to tell the query to SELECT Duplicate records properly according to my needs before creating the DELETE query.
Thanks Guys

Answer 1

You can use the following query to produce the required result set:
SELECT t1.*
FROM store AS t1
JOIN (
SELECT MIN(id) AS id, ref, item_no
FROM store
GROUP BY ref, item_no
) AS t2 ON t1.id > t2.id AND t1.ref = t2.ref AND t1.item_no = t2.item_no
Demo here
To DELETE you can use:
DELETE t1
FROM store AS t1
JOIN (
SELECT MIN(id) AS id, ref, item_no
FROM store
GROUP BY ref, item_no
) AS t2 ON t1.id > t2.id AND t1.ref = t2.ref AND t1.item_no = t2.item_no

Answer 2

To find only duplicate records you can use
SELECT * FROM store WHERE id NOT IN
(SELECT id FROM store AS outerStore WHERE id =
(SELECT MAX(id) FROM store AS innerStore
WHERE outerStore.ref = innerStore.ref AND
outerStore.supplier = innerStore.supplier AND outerStore.item_no = innerStore.item_no))
Maybe long, but it should work.

Answer 3

If you want the select of the row to delete use
select * from store
where id not in (
select max(id) from store
group by distinct ref, item_no, supplier);
Or you can directly use a command for direct delete using
delete from store
where id not in (
select max(id) from store
group by distinct ref, item_no, supplier);