Possible to do a delete with a HAVING clause?

Question

I want to do something like below:

DELETE UserPredictions
  GROUP BY UserId
  HAVING COUNT(*) < 500

But I\'m getting a syntax error. Is

Answer 1

Not really. The having clause implies an aggregation, which means you don't have the original rows any more.

I think you want the following:

DELETE from UserPredictions
where UserId in (select UserId from UserPredictions group by UserId having count(*) < 500)

Answer 2

I don't think that is possible however you can try this

Update : In as well as inner join can be used

Declare @Sample table 
(
UserID int,
col2 int
)
INSERT INTO @Sample
SELECT 1,50 UNION ALL
SELECT 1,100 UNION ALL
SELECT 2,150 UNION ALL
SELECT 2,200 union all
Select 4,500

DeLETE FROM @Sample  
WHERE UserID IN (SELECT UserID
             FROM @Sample 
             GROUP BY UserID
             HAVING COUNT(*) > 1)


 Delete O
 FROM @Sample O
 INNER JOIN 
 (
  SELECT UserID 
  FROM @Sample  
  GROUP BY UserID
 HAVING COUNT(*) >1
 ) X
ON O.UserID = X.UserID

The answer which i originally posted :

Delete O
FROM UserPredictions O
INNER JOIN 
(
 SELECT UserID 
 FROM UserPredictions  
 GROUP BY UserID
 HAVING COUNT(*) <500
 ) X
ON O.UserID = X.UserID

Answer 3

You can do so much with using row_number() OVER (partition by ) and CTE's, but only if your RDBMS supports it.

Example:

WITH CTE AS 
(
    SELECT UserId,
    ROW_NUMBER() OVER (PARTITION BY UserId ORDER BY UserId) AS rowcount    
    FROM UserPredictions
)
DELETE FROM CTE
WHERE rowcount < 500

Additional info about the row count function:

https://docs.microsoft.com/en-us/sql/t-sql/functions/row-number-transact-sql?view=sql-server-2017

Answer 4

Try this nested query:

DELETE FROM UserPredictions  
WHERE UserId IN (SELECT UserId
                 FROM UserPredictions 
                 GROUP BY UserId
                 HAVING COUNT(*) < 500)

Answer 5

You can use a joined subselect within the DELETE statement:

DELETE a
FROM   UserPredictions a
JOIN
(
    SELECT   UserId
    FROM     UserPredictions
    GROUP BY UserId
    HAVING   COUNT(1) < 500
) b ON a.UserId = b.UserId

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