7
\$\begingroup\$

I was interested in finding some of the weirdest question/protection combinations, basically out of curiosity.

I heuristically defined this as:

  • Low view counts
  • Not a moderator/SE employee
  • From users who protect multiple questions

I'm... let's just say not an expert in SQL. Though this query works, it feels super inefficient (especially the 2x left join, it seems plausible that could be a single join).

Looking basically for any feedback. I used this site to format things, so hopefully it's more readable than the mess it was before I started formatting it.

You can play with it here if your curiosity is also too strong to resist ;)


DECLARE @postViews int
SET @postViews = ##postView##
SELECT [Post Link] = ph.PostId,
       [User Link] = ph.UserId,
       Protected.ProtectCount,
       Unprotected.UnprotectedCount
FROM PostHistory ph
JOIN Posts p ON ph.PostID=p.id
LEFT JOIN
  (SELECT count(UserID) AS ProtectCount,
          PostID
   FROM PostHistory ph
   WHERE ph.PostHistoryTypeID=19
   GROUP BY PostID) AS Protected ON Protected.PostID=ph.PostID
LEFT JOIN
  (SELECT count(ph.UserID) AS UnprotectedCount,
          PostID
   FROM PostHistory ph
   WHERE ph.PostHistoryTypeID=20
   GROUP BY PostID) AS Unprotected ON Unprotected.PostID=ph.PostID
WHERE ph.UserID IN
    (SELECT top ##NumbUsers## ph.UserId
     FROM PostHistory ph
     JOIN Posts p ON ph.PostID=p.id
     WHERE ph.PostHistoryTypeId = 19
       AND p.ViewCount < @postViews 
       /* exclude former moderators */
       AND ph.UserID NOT IN (419,
                             1228,
                             1288,
                             19679,
                             23354,
                             50049,
                             59303,
                             102937,
                             106224,
                             246246,
                             -1)
     GROUP BY ph.UserId
     ORDER BY COUNT (ph.UserId) DESC)
  AND ph.PostHistoryTypeId = 19
  AND p.ClosedDate IS NULL
  AND p.ViewCount < @postViews
  AND isnull(Protected.ProtectCount,0) != isnull(Unprotected.UnprotectedCount,0)
ORDER BY ph.UserId
\$\endgroup\$
1
  • \$\begingroup\$ Oh, adapted for Workplace... that's why I don't see my userid there. \$\endgroup\$ – Simon Forsberg Jan 29 '16 at 9:09
4
\$\begingroup\$

One of the first things you should do if you have an arbitrary data set (as you do in your list of UserIds) would be to extract it out of the WHERE clause. Just make a @TempTable variable. If the data set gets very large, consider a "physical" #TempTable.

DECLARE @UsersToExclude TABLE (UserId INT PRIMARY KEY);
INSERT INTO @UsersToExclude (UserId) 
VALUES
  /*Some comments to explain these numbers would be good:*/
  (419),
  (1228),
  (1288),
  (19679),
  (23354),
  (50049),
  (59303),
  (102937),
  (106224),
  (246246),
  (-1);

Then you can just do an existence check in your query:

   AND ph.UserID NOT IN (
     SELECT usrExcl.UserID from @UsersToExclude as usrExcl
   )

Please get into the habit of using the (optional) keyword AS to reference to table aliases. If not used it can be ambiguous whether it's supposed to be an alias or a query hint for something else, like NOLOCK.

FROM PostHistory AS ph
  JOIN Posts AS p ON ph.PostID = p.id

This bracketing style is a bit unusual:

LEFT JOIN
  ( SELECT foo
   FROM bar
   WHERE ...) AS Unprotected ON Unprotected.PostID=ph.PostID

It looks like LISP-style brackets. Most often in SQL either C# or Java style brackets are used (depending on the programming shop).

C#-style

LEFT JOIN
(
    SELECT foo
    FROM bar
    WHERE ...
) 
AS Unprotected ON Unprotected.PostID=ph.PostID

Java-style

LEFT JOIN (
    SELECT foo
    FROM bar
    WHERE ...
) AS Unprotected ON Unprotected.PostID=ph.PostID

What does this number mean?

WHERE ph.PostHistoryTypeID=19

No easy way to tell. Consider something like:

DECLARE @QuestionProtected INT = (SELECT Id FROM PostHistoryTypes WHERE Name = 'Question Protected');

Then it's easier to follow:

WHERE ph.PostHistoryTypeID = @QuestionProtected

SEDE magic

You can get this valueat the top, or assign a default value for newbies like me:

-- postViews: Number of post views
DECLARE @postViews INT = ##postViews:int?10000##;

The other one is a script variable so it can't be manipulated as easily, but can still be assigned a default value (and documented):

WHERE 
  ph.UserID IN ( 
    -- NumbUsers: Max number of users
    SELECT TOP ##NumbUsers:int?5000## 

One more thing,

  AND isnull(Protected.ProtectCount,0) != isnull(Unprotected.UnprotectedCount,0)

The != operator is not SQL standard. Instead, use <>. Also, consider using COALESCE() instead of ISNULL() for some of the reasons listed here. Performance is right about the same, but it handles types better, usually (and can take more than 2 arguments, if needed).


Everything combined (demo on SEDE)

-- postViews: Number of post views
DECLARE @postViews INT = ##postViews:int?10000##;

DECLARE @UsersToExclude TABLE (UserId INT PRIMARY KEY);
DECLARE @QuestionProtected INT = (SELECT Id FROM PostHistoryTypes WHERE Name = 'Question Protected');
INSERT INTO 
  @UsersToExclude (UserId)
VALUES
  /*Some comments to explain these numbers would be good:*/
  (419),
  (1228),
  (1288),
  (19679),
  (23354),
  (50049),
  (59303),
  (102937),
  (106224),
  (246246),
  (-1);
SELECT 
  [Post Link] = ph.PostId,
  [User Link] = ph.UserId,
  Protected.ProtectCount,
  Unprotected.UnprotectedCount,
  p.ViewCount
FROM 
  PostHistory AS ph
  INNER JOIN 
    Posts AS p ON ph.PostID = p.id
  LEFT JOIN ( 
    SELECT 
      count(UserID) AS ProtectCount,
      PostID
    FROM PostHistory ph
    WHERE ph.PostHistoryTypeID = @QuestionProtected
      GROUP BY PostID
  ) AS Protected ON Protected.PostID = ph.PostID
  LEFT JOIN ( 
    SELECT 
      count(ph.UserID) AS UnprotectedCount,
      PostID
     FROM PostHistory ph
     WHERE ph.PostHistoryTypeID=20
     GROUP BY PostID
  ) AS Unprotected ON Unprotected.PostID = ph.PostID
WHERE 
  ph.UserID IN ( 
    -- NumbUsers: Max number of users
    SELECT TOP ##NumbUsers:int?5000## 
      ph.UserId
    FROM PostHistory ph
      JOIN Posts p ON ph.PostID=p.id
    WHERE ph.PostHistoryTypeId = @QuestionProtected
      AND p.ViewCount < @postViews /* exclude former moderators */
      AND ph.UserID NOT IN (
         SELECT usrExcl.UserID from @UsersToExclude as usrExcl
      )
    GROUP BY ph.UserId
    ORDER BY COUNT(ph.UserId) DESC
  )
  AND ph.PostHistoryTypeId = @QuestionProtected
  AND p.ClosedDate IS NULL
  AND p.ViewCount < @postViews
  AND COALESCE(Protected.ProtectCount,0) <> COALESCE(Unprotected.UnprotectedCount,0)
ORDER BY ph.UserId ASC;
\$\endgroup\$

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