WHERE/GROUP By Condition - 一个名称但多个值

Question

我有下表：

Name          Product         
Bob           Car              
Bob           Apples
Bob           Pears
Bob           Car
John          Apples
John          Pears

无论谁购买了 Product Car，我都希望与其他人保持距离。所以，我创建了一个标志：

Name          Product       Flag        
Bob           Car             1  
Bob           Apples          0
Bob           Pears           0  
Bob           Car             1
John          Apples          0
John          Pears           0 

但我的标志的问题在于，即使我执行 where 条件并说，向我展示消费者 WHERE 标志！=1，它也会选择 Bob。这是不正确的，因为 Bob 拥有汽车。

我仍想按产品分组。

如何将上表分成两组？

谢谢！

Answer 1

使用下面的查询：-

select name from table where flag!=1
and name not in (select name from table where flag = 1)
group by name

Answer 2

“告诉我消费者 WHERE 标志！=1，它会选择 Bob”，这是因为您要求 rows where flag != 1。相反，您需要更多的东西复杂的，比如：

SELECT DISTINCT Name
FROM tableTable
WHERE Name NOT IN (SELECT Name FROM theTable WHERE Product = 'Car')

或者，您可以执行 LEFT JOIN，这可能会或可能不会更快，具体取决于您拥有的数据量及其值的分布方式。

SELECT DISTINCT a.Name
FROM theTable a
LEFT JOIN theTable b ON a.Name = b.Name AND b.Product = 'Car'
WHERE a.Product != 'Car' AND b.Product IS NULL
;

这会获取除汽车以外的所有产品行，然后使用 LEFT JOIN 结合 IS NULL 条件来查找没有“汽车”行的行。

Answer 3

我认为您希望显示您的表的数据，只是以某种方式将“购买汽车的人”分区（未分组）分开 - 例如，这可以通过 ORDER BY OwnsACar 子句来完成。

第 1 步：确定购买汽车的人：

SELECT DISTINCT
    Name
FROM
    yourTable
 WHERE
    Product = 'Car'

第 2 步：加入此数据以生成计算得出的“OwnsACar”列：

SELECT
    yourTable.Name,
    yourTable.Product,
    ISNULL( carowners.Name ) AS OwnsACar
FROM
    yourTable
    LEFT OUTER JOIN
    (
        SELECT DISTINCT
        Name
    FROM
        yourTable
    WHERE
        Product = 'Car'
    ) AS carowners ON carowners.Name = yourTable.Name
ORDER BY
    OwnsACar ASC,
    yourTable.Name ASC

Answer 4

您可以使用这两个查询。不需要额外的Flag 列。

-- do not have Car
SELECT * 
FROM products
WHERE Name not in (SELECT DISTINCT Name 
                   FROM products 
                   WHERE Product='Car');

-- have Car
SELECT * 
FROM products
WHERE Name in (SELECT DISTINCT Name 
               FROM products 
               WHERE Product='Car');

插图：

-- table
SELECT * FROM products;
+------+---------+
| Name | Product |
+------+---------+
| Bob  | Car     |
| Bob  | Apples  |
| Bob  | Pears   |
| Bob  | Car     |
| John | Apples  |
| John | Pears   |
+------+---------+

-- query for people that do not have Car
+------+---------+
| Name | Product |
+------+---------+
| John | Apples  |
| John | Pears   |
+------+---------+


-- query for people having 'Car'
+------+---------+
| Name | Product |
+------+---------+
| Bob  | Car     |
| Bob  | Apples  |
| Bob  | Pears   |
| Bob  | Car     |
+------+---------+

Answer 5

尝试：

SELECT `t`.`Name`, `t`.`Product`, SUM(`t`.`Flag`) as hasCar
FROM your_table t
GROUP BY `t`.`Name`
HAVING `t`.`hasCar` = 0;

尽管您可以通过以下方式不使用标志列：

SELECT `t`.`Name`, `t`.`Product`, SUM(IF(`t`.`Product` = 'Car', 1, 0)) as hasCar
FROM your_table t
GROUP BY `t`.`Name`
HAVING `t`.`hasCar` = 0;