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SQL Select Concatenating rows avoiding double commas, where are the columns null?

I have the following reference data.

PERSON_NAME                    STREET                   TOWN             COUNTY           POSTCODE   
------------------------------ ------------------------ ---------------- ---------------- ---------- 
David Smith                    30 Johnson Street        Norwich          Norfolk          NA38 3KL   
John Brown                     Douglas Road             Cambridge                         C8  9IJ    
Jackie White                   8 High Street            Ipswich          Suffolk          IP7  2YT   
Andrea Blue                    9 Marlborough Ave        Bury             Suffolk          IP4  0XC   
Jemima Green                   Riverside Walk           Colchester       Essex            CO6  7PR   
James Gray                     167 Hadleigh Place       London                            SW1 4TU

What I want to do is display a list of the names of people along with their concatenated addresses in a comma separated line.

This part is simple, I used columns ||for concat and put comma separators.

The part I doubt about is that some lines don't have anything listed for COUNTY, so I need to avoid displaying , ,.

SUBSTR Oracle , "". , ( SO)?

, :

SELECT
    SUPPNAME as "Supplier Name",
    REPLACE(STREET || ', ' || TOWN || ', ' || COUNTY || ', ' || POSTCODE, ' ,','') as "Supplier Address"
FROM
    SUPPLIERS
;

+5
3

SELECT
SUPPNAME AS "Supplier Name",
(
CASE WHEN STREET IS NULL THEN '' ELSE STREET || ', ' END || 
CASE WHEN TOWN IS NULL THEN '' ELSE TOWN || ', ' END ||
CASE WHEN COUNTY IS NULL THEN '' ELSE COUNTY || ', ' END || 
CASE WHEN POSTCODE IS NULL THEN '' ELSE POSTCODE END
) AS "Supplier Address"
FROM SUPPLIERS
+7

, NULL, ',' NULL. , ","

SELECT
SUPPNAME AS "Supplier Name",
SUBSTR(
    NVL2(STREET, ', ' || STREET, NULL)
        || NVL2(TOWN, ', ' || TOWN, NULL)
        || NVL2(COUNTY, ', ' || COUNTY, NULL)
        || NVL2(POSTCODE, ', ' || POSTCODE, NULL)
    ,2) AS "Supplier Address"
FROM SUPPLIERS
+3

NVL2 , , - NVL2(county, county || ',', '')

+2
source

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