Question

假设我有一个MySQL表，其中包含以下条目;

ID,     PRODUCTID
95,     2
95,     2
95,     1
96,     1
102,    1
102,    5
95,     5

如何选择仅具有一个不同ID列值的PRODUCTID。

我想要回来的结果是：

PRODUCTID
2

我尝试了一些方法;

SELECT DISTINCT PRODUCTID
FROM `TABLE`
GROUP  BY ID, PRODUCTID
HAVING COUNT(*) = 1;

Answer 1

按productid分组，然后使用count(distinct id)计算唯一的id

SELECT PRODUCTID
FROM your_table
GROUP BY PRODUCTID
HAVING COUNT(distinct ID) = 1

Answer 2

SELECT DISTINCT x.PRODUCTID 
           FROM my_table x 
           LEFT 
           JOIN my_table y 
             ON y.PRODUCTID = x.PRODUCTID 
            AND y.ID <> x.ID 
          WHERE y.ID IS NULL;

Answer 3

COUNT(DISTINCT)是解决此问题的一种方法。但是，我更愿意比较MIN()和MAX() - 因为这些计算成本更低：

SELECT PRODUCTID
FROM `TABLE`
GROUP BY PRODUCTID
HAVING MIN(ID) = MAX(ID);

如果ID可能是NULL，则需要添加其他条件：

SELECT PRODUCTID
FROM `TABLE`
GROUP BY PRODUCTID
HAVING (MIN(ID) = MAX(ID) AND COUNT(*) = COUNT(ID)) OR  -- No NULL values
        (MIN(ID) IS NULL);                              -- or all NULL values

Answer 4

ID,     PRODUCTID
95,     2
95,     2
95,     1
96,     1
102,    1
102,    5
95,     5
you can use this this is working fine
SELECT distinct product_id from  category GROUP  BY id, product_id
HAVING COUNT(*) = 1;

SQL选择不同的列值

4 个答案: