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find unique value from a three way join

Posted on 2008-10-29
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Last Modified: 2012-05-05
Trying to capture processes taking io and need to select distiinct spid from the query.  Was trying to select it into a temp table, but not allowed due to 'NULL' values.  Using distinct also isn't helping.  I must be doing my join incorrectly but unsure how to proceed... it has to be something elementary.

     select convert (char(19), getdate()),
                convert (char(15), b.name) as login,
                convert (char(15), c.name) as dbname,
                convert  (char(4), a.spid) as spid,
                                             a.status,
                                             acmd,
                                             a.physical_io,
               convert  (char(5), a.cpu) as cpu,
               convert  (char(5), a.blocked) as block,
               convert  (char(5), a.time_blocked) as time

    from master..sysprocesses   a,
            master..syslogins           b,
            master..sysdatabases   c

    where physical_io > 0
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Question by:sanate
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LVL 6

Expert Comment

by:RPCIT
ID: 22833169
The SQL you wrote has some basic problems that I see, for instance you don't have any relations defined, but this could just be because I use MSSQL 2000 and 2005.  

But regardless, you should be able to wrap the whole thing (assuming your happy with the results) with
   SELECT DISTINCT spid FROM ( YOUR_SQL_HERE ) subQueryAlias

hope this helps.
SELECT DISTINCT spid FROM (
	       select convert (char(19) , getdate() )AS _now,
                convert (char(15), b.name) as login,
                convert (char(15), c.name) as dbname,
                convert  (char(4), a.spid) as spid,
                                             a.status,
                                             a.cmd,
                                             a.physical_io,
               convert  (char(5), a.cpu) as cpu,
               convert  (char(5), a.blocked) as block--,
               --convert  (char(5), a.time_blocked) as time
 
    from master..sysprocesses   a,
            master..syslogins           b,
            master..sysdatabases   c
 
    where physical_io > 0) sub

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Author Comment

by:sanate
ID: 22833391
Thanks for looking into this.  But we've been having some issues tracking logins giving the databases angst.  This solution does indeed work for isolating unique spids... but also need to capture the other columns in the select statement.  By the unique statement I'm getting a row returned for every database... so its returning in this case 15 rows for every spid.
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LVL 6

Expert Comment

by:RPCIT
ID: 22833711
you just need to add the fields that you want to see, and then some aggregate function for the others.  If you want all the fields, then distict will only work where all the fields are identical.

SELECT DISTICT spid, MAX(Login) as Login FROM (.....) alias GROUP BY spid

would do a rollup, and only give you spids, but you would lost detail on the login field.
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Accepted Solution

by:
grant300 earned 500 total points
ID: 22833896
The problem is you are not specifying the join SARGs in the WHERE clause so you are getting a Cartesian product; A x B x C rows total.  You have to join the suid in the sysprocesses table to the suid in syslogins and the dbid in sysprocesses to the dbid in sysdatabases.

I personally prefer to use the ANSI SQL syntax for joins as they are less ambiguous and easier to read.  See the snippet.

Regards,
Bill

  select convert (char(19), getdate()),
         convert (char(15), b.name) as login,
         convert (char(15), c.name) as dbname,
         convert  (char(4), a.spid) as spid,
         a.status,
         a.cmd,
         a.physical_io,
         convert  (char(5), a.cpu) as cpu,
         convert  (char(5), a.blocked) as block,
         convert  (char(5), a.time_blocked) as time
    from master..sysprocesses   a
    join master..syslogins      b
      on b.suid = a.suid
    join master..sysdatabases   c
      on c.dbid = a.dbid
   where physical_io > 0

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Author Closing Comment

by:sanate
ID: 31511270
Thanks much, don't know why I was drawing a blank on that.  Must have wasted half of yesterday on it.
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