如何编写SQL查询按邮政编码拆分州？以马里兰分东西为例

Got it, here's how you can split Maryland into the two required regions while keeping all other states intact in your aggregation:

Solution SQL Query #

SELECT 
    CASE
        -- Handle Maryland's regional split
        WHEN State = 'Maryland' THEN
            CASE
                WHEN LEFT(CAST(zip AS VARCHAR), 3) IN ('216', '218', '219') THEN 'MD East'
                ELSE 'MD West'
            END
        -- Keep all other states as-is
        ELSE State
    END AS Region,
    SUM(Revenue) AS TotalRevenue
FROM your_table_name
GROUP BY 
    CASE
        WHEN State = 'Maryland' THEN
            CASE
                WHEN LEFT(CAST(zip AS VARCHAR), 3) IN ('216', '218', '219') THEN 'MD East'
                ELSE 'MD West'
            END
        ELSE State
    END
ORDER BY Region;

Key Details Explained #

• CASE Statement Logic: The outer CASE checks if the row belongs to Maryland. If yes, the inner CASE evaluates the first 3 characters of the zip code to assign it to either MD East or MD West. All other states retain their original names.
• Zip Code Handling: CAST(zip AS VARCHAR) ensures we can safely use the LEFT() function even if your zip field is stored as a numeric type (like INT). If your zip is already a string column, you can simplify this to LEFT(zip, 3).
• Group Consistency: The GROUP BY clause mirrors the exact CASE logic from the SELECT statement—this is critical to ensure the aggregation groups correctly by your new regional labels.
• Result Count: This query will return 51 rows: 49 original states (excluding Maryland) plus MD East and MD West, which matches your requirement.

Quick Notes #

• Double-check that the state name in your table matches 'Maryland' (case sensitivity depends on your database configuration).
• Any Maryland zip codes not starting with 216, 218, or 219 will automatically fall into MD West, as requested.

内容的提问来源于stack exchange，提问作者brendensmall