Question

我想根据以下列获取输出。让我知道我应该如何实现它。

我必须在where子句中将类别与merchantcategory进行比较。

Table A, `Category` (with example data):

Travel              | Gas | Restaurant  | Spending
-------------------------------------------------------
All Other Merchants | gas | Hotel       | Credit Card 
U.S. Post Exchange  | gas | Motel       | Bill Payment


Table B, `MerchantCategory` columns:

College/School Expense
Hospital
Gas
Pre-Authorized Mail/Telephone Order
Hotel/Motel
Shopping
Credit Card Bill Payment
Grossary
All Other Merchants/U.S. Post Exchange
Restaurant

那么我应该如何通过将单独的列添加为id来实现它呢？

或者通过案例或其他方式使用？

Answer 1

在每个类别值之间创建一个链接，可能在临时表中。

IF OBJECT_ID('tempdb..#CategoryConversions') IS NOT NULL
    DROP TABLE #CategoryConversions

CREATE TABLE #CategoryConversions (
    MerchantCategory VARCHAR(100),
    Category VARCHAR(100))

INSERT INTO #CategoryConversions (
    MerchantCategory,
    Category)
VALUES
    ('gas', 'gas'),
    ('Spending', 'Grossary '),
    ('Spending', 'Credit Card Bill Payment'),
    ('Restaurant', 'Hotel/Motel')
    --.....

现在加入所有3个：

SELECT
    YourWantedColumns
FROM
    TableA AS A
    INNER JOIN #CategoryConversions AS C ON A.Category = C.Category
    INNER JOIN TableB AS B ON C.MerchantCategory = B.MerchantCategory

如果您想避开临时表，可以使用以下方法：

;WITH CategoryConversions AS
(
    SELECT
        C.MerchantCategory,
        C.Category
    FROM
        (VALUES 
            ('gas', 'gas'),
            ('Spending', 'Grossary '),
            ('Spending', 'Credit Card Bill Payment'),
            ('Restaurant', 'Hotel/Motel')
            --......
        ) AS C(MerchantCategory, Category)
)
SELECT
    YourWantedColumns
FROM
    TableA AS A
    INNER JOIN CategoryConversions AS C ON A.Category = C.Category
    INNER JOIN TableB AS B ON C.MerchantCategory = B.MerchantCategory

SQL：使用不同的数据比较两个不同的列

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