让SUM和JOIN在特定查询中合作

Question

我坚持使用某个查询，它似乎很简单，但似乎我可能不得不以不同的方式拆分它以实现我想要做的事情。我尝试了组合，重组，我可以使用一些指导。

这是一个示例表，输出和预期输出。

Shop_Table

shop_id |     item_type  | date

   1          soaps         2000-01-01
   2          food          2000-01-02
   3          appliances    2000-01-03
   4          electronics   2000-01-10
   5          furniture     2000-01-13
   6          misc.         2000-01-15

Instance_Table

instanceid|    shop_id    | firstname | lastname | number_of_items

   11            3            jane        doe          2
   22            2            jane        doe          3
   33            1            jane        doe          5
   44            4            jane        doe          6
   55            6            jane        doe          1
   66            5            jane        doe          2

查询

SELECT 
IF
( 
    Shop_Table.item_type
    IN
        (
            'soaps',
            'food'
         ),
    'indexpensives',
    Shop_Table.item_type
), 
COALESCE(SUM(Person.number_of_items), 0) AS item_sum
FROM Shop_Table

INNER JOIN Instance_Table AS Instance
ON Instance.shop_id = Shop_Table.shop_id
AND Instance.firstname =  'jane'
AND Instance.lastname =  'doe'
AND Shop_Table.date BETWEEN DATE(  '2000-01-01' ) AND DATE(  '2000-01-03' )

GROUP BY Shop_Table.item_type

返回：

  item_type     |     item_sum

indexpensives   |        8
appliances      |        2

输出

到目前为止哪个很棒，而且是我被困的地方。我真正想要的是以下输出：

预期产出

  item_type     |     item_sum

inexpensives    |        8
appliances      |        2
electronics     |        0
furniture       |        0
misc.           |        0

我认为我想要做的事情非常简单。让它变得有点艰难的是它有一点点的东西。

• 对总和结果进行分组和组合（肥皂和食物合并为一个结果）
• 当日期超出指定范围时，为其余项目类型返回0。

更新

比我想象的要复杂一点，但这就是我想要的。谢谢大家的帮助。

SELECT 
IF
( 
    Shop_Table.item_type
    IN
        (
            'soaps',
            'food'
         ),
    'inexpensives',
    Shop_Table.item_type
), 
COALESCE(SUM(Person.number_of_items), 0) AS item_sum
FROM Shop_Table
LEFT OUTER JOIN Instance_Table AS Instance
ON Instance.shop_id = Shop_Table.shop_id
AND Instance.firstname =  'jane'
AND Instance.lastname =  'doe'
AND Shop_Table.date BETWEEN DATE(  '2000-01-01' ) AND DATE(  '2000-01-03' )
GROUP BY IF
( 
    Shop_Table.item_type
    IN
        (
            'soaps',
            'food'
         ),
    'inexpensives',
    Shop_Table.item_type
)

Answer 1

将您的查询更改为此，您应该获得您正在寻找的总数：

SELECT 
IF
( 
    Shop_Table.item_type
    IN
        (
            'soaps',
            'food'
         ),
    'indexpensives',
    Shop_Table.item_type
), 
SUM(Person.number_of_items) AS item_sum
FROM Shop_Table

LEFT OUTER JOIN Instance_Table AS Instance
ON Instance.shop_id = Shop_Table.shop_id
AND Instance.firstname =  'jane'
AND Instance.lastname =  'doe'
AND Shop_Table.date BETWEEN DATE(  '2000-01-01' ) AND DATE(  '2000-01-03' )

GROUP BY Shop_Table.item_type

<强>解释
外连接将从一个表中选择所有行，并从另一个表中选择匹配的行。因此，LEFT OUTER JOIN将从连接左侧的表中选择所有行（在本例中为Shop_Table），并从连接右侧的表中匹配行（在本例中为Instance_Table）。

Answer 2

首先用inner join替换left join，然后确保coalesce sum为0，如下所示：

SELECT 
IF
( 
    Shop_Table.item_type
    IN
        (
            'soaps',
            'food'
         ),
    'indexpensives',
    Shop_Table.item_type
), 
COALESCE(SUM(Person.number_of_items), 0) AS item_sum
FROM Shop_Table
LEFT JOIN Instance_Table AS Instance
ON Instance.shop_id = Shop_Table.shop_id
AND Instance.firstname =  'jane'
AND Instance.lastname =  'doe'
AND Shop_Table.date BETWEEN DATE(  '2000-01-01' ) AND DATE(  '2000-01-03' )
GROUP BY Shop_Table.item_type

修改

需求更改后，这应该是最终查询：

SELECT 
IF
( 
    Shop_Table.item_type
    IN
        (
            'soaps',
            'food'
         ),
    'inexpensives',
    Shop_Table.item_type
) as FinalType, 
COALESCE(SUM(Person.number_of_items), 0) AS item_sum
FROM Shop_Table
LEFT OUTER JOIN Instance_Table AS Instance
ON Instance.shop_id = Shop_Table.shop_id
AND Instance.firstname =  'jane'
AND Instance.lastname =  'doe'
AND Shop_Table.date BETWEEN DATE(  '2000-01-01' ) AND DATE(  '2000-01-03' )
GROUP BY FinalType