Select multiple columns from a table, but group by one

I use this trick to group by one column when I have a multiple columns selection:

SELECT MAX(id) AS id,
    Nume,
    MAX(intrare) AS intrare,
    MAX(iesire) AS iesire,
    MAX(intrare-iesire) AS stoc,
    MAX(data) AS data
FROM Produse
GROUP BY Nume
ORDER BY Nume

This works.

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I just wanted to add a more effective and generic way to solve this kind of problems. The main idea is about working with sub queries.

do your group by and join the same table on the ID of the table.

your case is more specific since your productId is not unique so there is 2 ways to solve this.

I will begin by the more specific solution: Since your productId is not unique we will need an extra step which is to select DISCTINCT product ids after grouping and doing the sub query like following:

WITH CTE_TEST AS (SELECT productId, SUM(OrderQuantity) Total
                    FROM OrderDetails
                    GROUP BY productId)
SELECT DISTINCT(OrderDetails.ProductID), OrderDetails.ProductName, CTE_TEST.Total
FROM OrderDetails 
INNER JOIN CTE_TEST ON CTE_TEST.ProductID = OrderDetails.ProductID

this returns exactly what is expected

 ProductID     ProductName         Total
    1001          abc               12    
    1002          abc               23
    2002          xyz               8
    3004          ytp               15
    4001          aze               19

But there a cleaner way to do this. I guess that ProductId is a foreign key to products table and i guess that there should be and OrderId primary key (unique) in this table.

in this case there are few steps to do to include extra columns while grouping on only one. It will be the same solution as following

Let's take this t_Value table for example:

https://i.stack.imgur.com/9SCl5.png

If i want to group by description and also display all columns.

All i have to do is:

create WITH CTE_Name subquery with your GroupBy column and COUNT condition select all(or whatever you want to display) from value table and the total from the CTE INNER JOIN with CTE on the ID(primary key or unique constraint) column

and that's it!

Here is the query

WITH CTE_TEST AS (SELECT Description, MAX(Id) specID, COUNT(Description) quantity 
                    FROM sch_dta.t_value
                    GROUP BY Description)
SELECT sch_dta.t_Value.*, CTE_TEST.quantity 
FROM sch_dta.t_Value 
INNER JOIN CTE_TEST ON CTE_TEST.specID = sch_dta.t_Value.Id

And here is the result:

https://i.stack.imgur.com/HtIlC.png

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Your Data

DECLARE @OrderDetails TABLE 
(ProductID INT,ProductName VARCHAR(10), OrderQuantity INT)

INSERT INTO @OrderDetails VALUES
(1001,'abc',5),(1002,'abc',23),(2002,'xyz',8),
(3004,'ytp',15),(4001,'aze',19),(1001,'abc',7)

Query

 Select ProductID, ProductName, Sum(OrderQuantity) AS Total
 from @OrderDetails 
 Group By ProductID, ProductName  ORDER BY ProductID

Result

╔═══════════╦═════════════╦═══════╗
║ ProductID ║ ProductName ║ Total ║
╠═══════════╬═════════════╬═══════╣
║      1001 ║ abc         ║    12 ║
║      1002 ║ abc         ║    23 ║
║      2002 ║ xyz         ║     8 ║
║      3004 ║ ytp         ║    15 ║
║      4001 ║ aze         ║    19 ║
╚═══════════╩═════════════╩═══════╝

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mysql GROUP_CONCAT function could help https://dev.mysql.com/doc/refman/8.0/en/group-by-functions.html#function_group-concat

SELECT ProductID, GROUP_CONCAT(DISTINCT ProductName) as Names, SUM(OrderQuantity)
FROM OrderDetails GROUP BY ProductID

This would return:

ProductID     Names          OrderQuantity
1001          red            5
1002          red,black      6
1003          orange         8
1004          black,orange   15

Similar idea as the one @Urs Marian here posted https://stackoverflow.com/a/38779277/906265

---

    WITH CTE_SUM AS (
      SELECT ProductID, Sum(OrderQuantity) AS TotalOrderQuantity 
      FROM OrderDetails GROUP BY ProductID
    )
    SELECT DISTINCT OrderDetails.ProductID, OrderDetails.ProductName, OrderDetails.OrderQuantity,CTE_SUM.TotalOrderQuantity 
    FROM 
    OrderDetails INNER JOIN CTE_SUM 
    ON OrderDetails.ProductID = CTE_SUM.ProductID

Please check if this works.

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You can try this:

Select ProductID,ProductName,Sum(OrderQuantity) 
 from OrderDetails Group By ProductID, ProductName

You're only required to Group By columns that doesn't come with an aggregate function in the Select clause. So you can just use Group By ProductID and ProductName in this case.

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You can try the below query. I assume you have a single table for all your data.

SELECT OD.ProductID, OD.ProductName, CalQ.OrderQuantity
FROM (SELECT DISTINCT ProductID, ProductName
      FROM OrderDetails) OD
INNER JOIN (SELECT ProductID, OrderQuantity SUM(OrderQuantity)
            FROM OrderDetails
            GROUP BY ProductID) CalQ
ON CalQ.ProductID = OD.ProductID

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In my opinion this is a serious language flaw that puts SQL light years behind other languages. This is my incredibly hacky workaround. It is a total kludge but it always works.

Before I do I want to draw attention to @Peter Mortensen's answer, which in my opinion is the correct answer. The only reason I do the below instead is because most implementations of SQL have incredibly slow join operations and force you to break "don't repeat yourself". I need my queries to populate fast.

Also this is an old way of doing things. STRING_AGG and STRING_SPLIT are a lot cleaner. Again I do it this way because it always works.

-- remember Substring is 1 indexed, not 0 indexed
SELECT ProductId
  , SUBSTRING (
      MAX(enc.pnameANDoq), 1, CHARINDEX(';', MAX(enc.pnameANDoq)) - 1
    ) AS ProductName
  , SUM ( CAST ( SUBSTRING (
      MAX(enc.pnameAndoq), CHARINDEX(';', MAX(enc.pnameANDoq)) + 1, 9999
    ) AS INT ) ) AS OrderQuantity
FROM (
    SELECT CONCAT (ProductName, ';', CAST(OrderQuantity AS VARCHAR(10)))
      AS pnameANDoq, ProductID
    FROM OrderDetails
  ) enc
GROUP BY ProductId

Or in plain language :

Glue everything except one field together into a string with a delimeter you know won't be used

Use substring to extract the data after it's grouped

Performance wise I have always had superior performance using strings over things like, say, bigints. At least with microsoft and oracle substring is a fast operation.

This avoids the problems you run into when you use MAX() where when you use MAX() on multiple fields they no longer agree and come from different rows. In this case your data is guaranteed to be glued together exactly the way you asked it to be.

To access a 3rd or 4th field, you'll need nested substrings, "after the first semicolon look for a 2nd". This is why STRING_SPLIT is better if it is available.

Note : While outside the scope of your question this is especially useful when you are in the opposite situation and you're grouping on a combined key, but don't want every possible permutation displayed, that is you want to expose 'foo' and 'bar' as a combined key but want to group by 'foo'

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==EDIT==

I checked your question again and have concluded this can't be done.

ProductName is not unique, It must either be part of the Group By or excluded from your results.

For example how would SQL present these results to you if you Group By only ProductID?

ProductID | ProductName | OrderQuantity 
---------------------------------------
1234      | abc         | 1
1234      | def         | 1
1234      | ghi         | 1
1234      | jkl         | 1

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I had a similar problem to the OP. Then I saw the answer from @Urs Marian which helped a lot. But additionally what I was looking for is, when there are multiple values in a column and they will be grouped, how I can get the last submitted value (e.g. ordered by a date/id column).

Example:

We have following table structure:

CREATE TABLE tablename(
    [msgid] [int] NOT NULL,
    [userid] [int] NOT NULL,
    [username] [varchar](70) NOT NULL,
    [message] [varchar](5000) NOT NULL
) 

Now there are at least two datasets in the table:

+-------+--------+----------+---------+
| msgid | userid | username | message |
+-------+--------+----------+---------+
|     1 |      1 | userA    | hello   |
|     2 |      1 | userB    | world   |
+-------+--------+----------+---------+

Therefore following SQL script does work (checked on MSSQL) to group it, also if the same userid has different username values. In the example below, the username with the highest msgid will be shown:

SELECT m.userid, 
(select top 1 username from table where userid = m.userid order by msgid desc) as username,
count(*) as messages
FROM tablename m
GROUP BY m.userid
ORDER BY count(*) DESC

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The elegant way of having your desired results, is by using 'over (partion by)' sql clause in the following way:

SELECT ProductID,ProductName,OrderQuantity
    ,SUM(OrderQuantity)     OVER(PARTITION BY ProductID) AS 'Total'
    --,AVG(OrderQuantity)   OVER(PARTITION BY ProductID) AS 'Avg'
    --,COUNT(OrderQuantity) OVER(PARTITION BY ProductID) AS 'Count'
    --,MIN(OrderQuantity)   OVER(PARTITION BY ProductID) AS 'Min'
    --,MAX(OrderQuantity)   OVER(PARTITION BY ProductID) AS 'Max'
FROM OrderDetails

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SELECT ProductID, ProductName, OrderQuantity, SUM(OrderQuantity) FROM OrderDetails WHERE(OrderQuantity) IN(SELECT SUM(OrderQuantity) FROM OrderDetails GROUP BY OrderDetails) GROUP BY ProductID, ProductName, OrderQuantity;

I used the above solution to solve a similar problem in Oracle12c.

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