I have a query that gives expected results. But for some use case I need the shipping address primary key. The below query gives me 10 result. But if I add shippadd.nkey in SELECT and in GROUP BY clause, it only gives 1 result. Can't we group by the nkey?

SELECT 
  t.entity AS customer_internal_id, 
  c.entityid AS customer_id, 
  c.companyName AS customer_name, 
  t.shipdate AS shipping_date, 
  l.id AS location_internal_id, 
  l.name AS location, 
  shipadd.addrtext AS shipping_address, 
  COUNT(t.id) AS count_of_order, 
  SUM(t.custbody_oc_pallet_quantity) AS total_pallet_quantity, 
FROM 
  transaction AS t 
  INNER JOIN customer AS c ON t.entity = c.id 
  INNER JOIN TransactionLine AS line ON line.Transaction = t.id 
  INNER JOIN location AS l ON line.location = l.id 
  INNER JOIN TransactionShipment AS tranship ON t.ID = tranship.Doc 
  INNER JOIN transactionShippingAddress AS shipadd ON t.shippingaddress = shipadd.nkey 
WHERE 
  t.type = 'SalesOrd' 
  AND BUILTIN.DF (t.status) IN (
    'Sales Order : Pending Fulfillment'
  ) 
  AND line.mainline = 'T' 
  AND t.shipdate IS NOT NULL 
  AND tranship.shippingmethod IN ('x1 Carrier', 'x2 Carrier') 
GROUP BY 
  t.entity, 
  c.entityid, 
  c.companyName, 
  t.shipdate, 
  l.id, 
  l.name, 
  shipadd.addrtext 
HAVING 
  SUM(t.custbody_oc_pallet_quantity) > '7' 
  AND COUNT(t.id) > '1' 
ORDER BY 
  t.shipdate, 
  shipadd.addrtext

Is it possible that only one address fits the bill, and you're getting 10 results because there are multiple other records in your JOINs that match that single address?

No, 8 out of those 10 address are unique. I have grouped already by the shipadd.addrtext. So after that grouping only I am getting 10 rows, but the moment I add the corresponding nkey in the select and group by clause, only 1 result comes back, remaining 9 just disappears.