我如何（或可以）在多个列上选择 DISTINCT？

我需要从表中检索所有行，其中两列的组合都不同。因此，我希望同一天没有任何其他销售的所有销售都以相同的价格进行。基于日期和价格的唯一销售将更新为活动状态。

所以我在想：

UPDATE sales
SET status = 'ACTIVE'
WHERE id IN (SELECT DISTINCT (saleprice, saledate), id, count(id)
             FROM sales
             HAVING count = 1)

但再往前走我的脑子就痛了。

SELECT DISTINCT a,b,c FROM t

is roughly相当于：

SELECT a,b,c FROM t GROUP BY a,b,c

习惯 GROUP BY 语法是个好主意，因为它更强大。

对于您的查询，我会这样做：

UPDATE sales
SET status='ACTIVE'
WHERE id IN
(
    SELECT id
    FROM sales S
    INNER JOIN
    (
        SELECT saleprice, saledate
        FROM sales
        GROUP BY saleprice, saledate
        HAVING COUNT(*) = 1 
    ) T
    ON S.saleprice=T.saleprice AND s.saledate=T.saledate
 )