SQL-如何在SQL中仅一次显示按列分组

Question

I have 3 columns Country, state, city in table.

I want city list with country and state.

I want to display result like single country name, with respect to state with multiple cities.

I did group by on country and state which display all country and state in each row. but I want only single country name and state name like this

Country  State        City
--------------------------------
India    Maharashtra  Mumbai
                      Pune
                      Nagpur
         Gujrat       Surat
                      ahmedabad
USA      New york     Albany
                      New york City
         california   Los angles

Answer 1

Have you tried:

SELECT DISTINCT country, state, city FROM table
GROUP BY country ASC, state ASC
ORDER BY country ASC, state ASC, city ASC;

That would return only distinct values from each column.

Answer 2

As @Gordon said it is better to do this in application layer once you fetched the data.

But if you really want to do this in sql, here is one solution.

;WITH All_Data AS (

    SELECT 
          COUNTRY,
          STATE,
          CITY
    FROM 
          TABLE_NAME
    GROUP BY 
          COUNTRY,
          STATE,
          CITY
--which gives all countries, states and cities.
),
Grouped_by_Country AS (

    SELECT 
          *,
           ROW_NUMBER () OVER(PARTITION BY COUNTRY ORDER BY STATE ) AS COUNTRY_NO
    FROM 
         All_Data

),
Grouped_by_State AS (

    SELECT 
          *,
          ROW_NUMBER() OVER(PARTITION BY COUNTRY,STATE ORDER BY CITY ) AS STATE_NO
    FROM 
         Grouped_by_Country

) ,

Result AS (

    SELECT 
          CASE WHEN COUNTRY_NO = 1
               THEN COUNTRY
               ELSE ''
          END AS COUNTRY,

          CASE WHEN STATE_NO = 1
               THEN STATE
               ELSE ''
          END AS STATE,

          CITY,
          COUNTRY_NO,
          STATE_NO

)

SELECT 
      COUNTRY,
      STATE,
      CITY

FROM 
      Result 
ORDER BY 
      COUNTRY_NO,
      STATE_NO