SQL对不同列中按相同值分组的计数进行除法运算

Question

所以我有一个表，其中有两行包含名称和其他内容，这两列可以包含相同的名称：

RegionID约翰·康尼

买方		卖方
John
Lina	Kajsa	2
Kajsa	康尼	3
John	Erik
Kajsa	康尼约翰·康尼
John约翰·康尼
Kajsa	David
David

SELECT clinetname,
Sum(buyercount) / Sum(sellercount)
FROM   (SELECT buyer    AS ClinetName,
Count(1) AS BuyerCount,
0        AS SellerCount
FROM   Store
WHERE  regionid = 1
GROUP  BY buyer
UNION ALL
SELECT seller   AS ClinetName,
0        AS BuyerCount,
Count(1) AS SellerCount
FROM   Store
WHERE  regionid = 1
GROUP  BY seller) a
GROUP  BY clinetname
HAVING Sum(sellercount) > 0;