我正在尝试列出下订单的客户名称,这些客户来自某个县并从某个销售代表处下订单。问题是,最终表格多次打印出他们的名字。如何让他们只打印一次名称?
SELECT cName
FROM customer INNER JOIN orders ON customer.cNo = orders.cNO,author
WHERE county = "Galway" AND saleRepName = "Jane Smith";
答案 0 :(得分:2)
您可以使用Distinct
,但如果有大量记录,您可能会受到性能影响
SELECT DISTINCT
cName
FROM customer
INNER JOIN orders ON customer.cNo = orders.cNO,author
WHERE county = "Galway" AND saleRepName = "Jane Smith";
Group By
可能会更快,并且可以让您获得计数:
SELECT
count(1),
cName
FROM customer
INNER JOIN orders ON customer.cNo = orders.cNO,author
WHERE county = "Galway" AND saleRepName = "Jane Smith";
GROUP BY cName
这将打印出如下内容:
3 John Doe
6 Jane Smith
1 Jersey Mike