Nsryjdtyk

Edit: Altered from the less-than-reliable checksum-only query
I've discovered a way to do this (in SQL Server 2005) that works pretty well for me and I can use as many columns as I need (by adding them to the CHECKSUM() function). The REVERSE() function turns the ints into varchars to make the distinct more reliable

SELECT COUNT(DISTINCT (CHECKSUM(DocumentId,DocumentSessionId)) + CHECKSUM(REVERSE(DocumentId),REVERSE(DocumentSessionId)) )

FROM DocumentOutPutItems

What is it about your existing query that you don't like? If you are concerned that DISTINCT across two columns does not return just the unique permutations why not try it?

It certainly works as you might expect in Oracle.

SQL> select distinct deptno, job from emp

  2  order by deptno, job

  3  /



    DEPTNO JOB

---------- ---------

        10 CLERK

        10 MANAGER

        10 PRESIDENT

        20 ANALYST

        20 CLERK

        20 MANAGER

        30 CLERK

        30 MANAGER

        30 SALESMAN



9 rows selected.





SQL> select count(*) from (

  2  select distinct deptno, job from emp

  3  )

  4  /



  COUNT(*)

----------

         9



SQL>

edit

I went down a blind alley with analytics but the answer was depressingly obvious...

SQL> select count(distinct concat(deptno,job)) from emp

  2  /



COUNT(DISTINCTCONCAT(DEPTNO,JOB))

---------------------------------

                                9



SQL>

edit 2

Given the following data the concatenating solution provided above will miscount:

col1  col2

----  ----

A     AA

AA    A

So we to include a separator...

select col1 + '*' + col2 from t23

/

Obviously the chosen separator must be a character, or set of characters, which can never appear in either column.

How about something like:

select count(*)

from

  (select count(*) cnt

   from DocumentOutputItems

   group by DocumentId, DocumentSessionId) t1

Probably just does the same as you are already though but it avoids the DISTINCT.

To run as a single query, concatenate the columns, then get the distinct count of instances of the concatenated string.

SELECT count(DISTINCT concat(DocumentId, DocumentSessionId)) FROM DocumentOutputItems;

In MySQL you can do the same thing without the concatenation step as follows:

SELECT count(DISTINCT DocumentId, DocumentSessionId) FROM DocumentOutputItems;

This feature is mentioned in the MySQL documentation:

http://dev.mysql.com/doc/refman/5.7/en/group-by-functions.html#function_count-distinct

Here's a shorter version without the subselect:

SELECT COUNT(DISTINCT DocumentId, DocumentSessionId) FROM DocumentOutputItems

It works fine in MySQL, and I think that the optimizer has an easier time understanding this one.

Edit: Apparently I misread MSSQL and MySQL - sorry about that, but maybe it helps anyway.

There's nothing wrong with your query, but you could also do it this way:

WITH internalQuery (Amount)

AS

(

    SELECT (0)

      FROM DocumentOutputItems

  GROUP BY DocumentId, DocumentSessionId

)

SELECT COUNT(*) AS NumberOfDistinctRows

  FROM internalQuery

I found this when I Googled for my own issue, found that if you count DISTINCT objects, you get the correct number returned (I'm using MySQL)

SELECT COUNT(DISTINCT DocumentID) AS Count1, 

  COUNT(DISTINCT DocumentSessionId) AS Count2

  FROM DocumentOutputItems

if you had only one field to "DISTINCT", you could use:

SELECT COUNT(DISTINCT DocumentId) 

FROM DocumentOutputItems

and that does return the same query plan as the original, as tested with SET SHOWPLAN_ALL ON. However you are using two fields so you could try something crazy like:

    SELECT COUNT(DISTINCT convert(varchar(15),DocumentId)+'|~|'+convert(varchar(15), DocumentSessionId)) 

    FROM DocumentOutputItems

but you'll have issues if NULLs are involved. I'd just stick with the original query.

Hope this works i am writing on prima vista

SELECT COUNT(*) 

FROM DocumentOutputItems 

GROUP BY DocumentId, DocumentSessionId

I wish MS SQL could also do something like COUNT(DISTINCT A, B). But it can't.

At first JayTee's answer seemed like a solution to me bu after some tests CHECKSUM() failed to create unique values. A quick example is, both CHECKSUM(31,467,519) and CHECKSUM(69,1120,823) gives the same answer which is 55.

Then I made some research and found that Microsoft does NOT recommend using CHECKSUM for change detection purposes. In some forums some suggested using

SELECT COUNT(DISTINCT CHECKSUM(value1, value2, ..., valueN) + CHECKSUM(valueN, value(N-1), ..., value1))

but this is also not conforting.

You can use HASHBYTES() function as suggested in TSQL CHECKSUM conundrum. However this also has a small chance of not returning unique results.

I would suggest using

SELECT COUNT(DISTINCT CAST(DocumentId AS VARCHAR)+'-'+CAST(DocumentSessionId AS VARCHAR)) FROM DocumentOutputItems

Many (most?) SQL databases can work with tuples like values so you can just do:

SELECT COUNT(DISTINCT (DocumentId, DocumentSessionId))
FROM DocumentOutputItems;

If your database doesn't support this, it can be simulated as per @oncel-umut-turer's suggestion of CHECKSUM or other scalar function providing good uniqueness e.g.

COUNT(DISTINCT CONCAT(DocumentId, ':', DocumentSessionId)).

A related use of tuples is performing IN queries such as:

SELECT * FROM DocumentOutputItems
WHERE (DocumentId, DocumentSessionId) in (('a', '1'), ('b', '2'));


It works for me. In oracle:

SELECT SUM(DECODE(COUNT(*),1,1,1))

FROM DocumentOutputItems GROUP BY DocumentId, DocumentSessionId;

In jpql:

SELECT SUM(CASE WHEN COUNT(i)=1 THEN 1 ELSE 1 END)

FROM DocumentOutputItems i GROUP BY i.DocumentId, i.DocumentSessionId;

How about this,

Select DocumentId, DocumentSessionId, count(*) as c 

from DocumentOutputItems 

group by DocumentId, DocumentSessionId;

This will get us the count of all possible combinations of DocumentId, and DocumentSessionId

You can just use the Count Function Twice.

In this case, it would be:

SELECT COUNT (DISTINCT DocumentId), COUNT (DISTINCT DocumentSessionId) 

FROM DocumentOutputItems

select DISTINCT DocumentId as i, DocumentSessionId as s , count(*)

from DocumentOutputItems

group by i ,s;

This code uses distinct on 2 parameters and provides count of number of rows specific to those distinct values row count. It worked for me in mysql like a charm.