Question

I’ve got the following reference data.

STORE_CODE      SUPPLIER_CODE
------          ------
ASDA            A3
ASDA            A2
TESCO           A2
TESCO           A4
ASDA            A4
ASDA            A4
ASDA            A4
ASDA            A4
WAITROSE        A3
ASDA            A4
WAITROSE        A3
ASDA            A3
ASDA            A3
ASDA            A4
SAINSBURY       A2
SAINSBURY       A2
SAINSBURY       A6
TESCO           A6
ASDA            A3
TESCO           A3
TESCO           A3
SAINSBURY       A3
WAITROSE        A5
WAITROSE        A5
WAITROSE        A5
WAITROSE        A4
ALDI            A1
ALDI            A1
ALDI            A1
ALDI            A1
ALDI            A1
ALDI            A1
ALDI            A1
ALDI            A1

What I want to do, is to display a list of suppliers, who have at least 4 unique stores associated to them.

So far, this is what I’ve conjugated :

SELECT 
    distinct stoc.supplier_code as SUPPLIER_CODE    
FROM 
        MYTABLE stoc
WHERE
    (select count(distinct a.store_code) from mytable a where a.supplier_code = stoc.supplier_code) >= 4
;

Is there anyway to optimize my select statement? The where clause looks rather messy and I was wondering if I can improve it by using GROUP BY or HAVING?

Many thanks

Answer 1

Try this:

SELECT COUNT(DISTINCT store_code), supplier_code
FROM myTable
GROUP BY supplier_code
HAVING COUNT(DISTINCT store_code) >= 4
ORDER BY 2