访问 SQL 多个 LEFT JOIN 无法工作

Question

表A

Shop ID	Item	Price
Shop A	Item1	101
Shop A	Item2	102
Shop A	Item3	103
Shop A	Item4	104
Shop A	Item5	105
Shop A	Item6	106
Shop A	Item7	107
......	.....	.....
Shop A	Item27	127
Shop B	Item1	201
Shop B	.....	.....
Shop B	Item27	227
Shop C	Item1	301
Shop C	.....	.....
Shop C	Item27	327

假设我有一个像上面那样的 table，我想在其中转换为下面的 table

Shop ID	Item1	Item2	Item3	Item4	.....	Item27
Shop A	101	102	103	104	.....	127

我尝试使用具有多个左连接的查询

SELECT T1.[Shop ID], T1.[Price] AS Item1 .... T27.[Price] AS Item 27

FROM (TableA AS T1
LEFT JOIN TableA AS T2 ON T1.[Shop ID] = T2.[Shop ID])
LEFT JOIN TableA AS T3 ON T1.[Shop ID] = T3.[Shop ID])
...
LEFT JOIN TableA AS T27 ON T1.[Shop ID] = T27.[Shop ID]

WHERE T1.[Item] = 'Item1'
AND T2.[Item] = 'Item2'
...
AND T27.[Item] = 'Item27'
AND T1.[Shop ID] = 'Shop A'

这适用于较少数量的 LEFT JOIN，但当 LEFT JOIN 的数量 > 20 时，访问基本上永远停止，我的实际 table 有点复杂。任何人都可以建议转换方法吗？ TIA

Answer 1

一种方法是使用数据透视查询：

SELECT
    [Shop ID],
    MAX(IIF([Item] = "Item1", Price, NULL)) AS Item1,
    MAX(IIF([Item] = "Item2", Price, NULL)) AS Item2,
    MAX(IIF([Item] = "Item3", Price, NULL)) AS Item3,
    ...
    MAX(IIF([Item] = "Item27", Price, NULL)) AS Item27
FROM TableA
GROUP BY [Shop ID]
ORDER BY [Shop ID];

您也可以使用 MS Access 查看交叉表选项。

Answer 2

像这样尝试交叉表查询-

TRANSFORM First(t.Price) AS FirstOfPrice
SELECT t.ShopID
FROM TableA as t
GROUP BY t.ShopID
ORDER BY t.Item
PIVOT t.Item;

输入：

输出：

访问 SQL 多个 LEFT JOIN 无法工作

Access SQL for multiple LEFT JOIN cant work

ms-access

left-join