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Sample Clause  After Filtering With A WHERE Clause with Table Joins

Posted on 2008-10-20
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Last Modified: 2013-12-18
Hello -

Im attempting to pull a 5% sample from the resulting dataset of a table join.  However, when trying to run this code I get an error.  I believe its because the sample clause is getting confused as to which table to sample.  Is there a way to get around this? What is the smartest way to get around this limitation of the Sample Clause?

Sample code below.

Thanks in advance.
SELECT a.Contact a.ContactNum b.Address c.Phone
FROM a.ExecInfo, b.Location, c.Demographics
SAMPLE(5)
WHERE a.LinkID = b.LinkID
   AND b.LinkID = c.LINKID;

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Question by:Keenetic
  • 2
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7 Comments
 
LVL 29

Accepted Solution

by:
MikeOM_DBA earned 125 total points
ID: 22759646

Try this:

WITH Q0 AS (
SELECT a.Contact a.ContactNum b.Address c.Phone
FROM a.ExecInfo, b.Location, c.Demographics
WHERE a.LinkID = b.LinkID
   AND b.LinkID = c.LINKID)
SELECT * FROM Q0 SAMPLE(5);

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LVL 29

Expert Comment

by:MikeOM_DBA
ID: 22759746

-- Or --
 Maybe you need to sample the largest table only:

WITH Q0 AS (
SELECT Contact, ContactNum, LinkID
  FROM ExecInfo SAMPLE(5))
SELECT a.Contact, a.ContactNum, b.Address c.Phone
  FROM Q0 a, b.Location, c.Demographics
 WHERE a.LinkID = b.LinkID
   AND b.LinkID = c.LINKID);

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Expert Comment

by:dxladner
ID: 22760302
The SAMPLE clause in ORACLE is basically:
SAMPLE(the number that you want )

The are some limitations to this clause: 1. Discrepancies in actual percentage in the returned data2. Using views and certain joins.  
0
 
LVL 4

Expert Comment

by:hqassap
ID: 22764949
Try this:

SELECT *
  FROM (SELECT a.contact, a.contactnum, b.address, c.phone
          FROM a.execinfo, b.LOCATION, c.demographics
         WHERE a.linkid = b.linkid AND b.linkid = c.linkid)
 WHERE ROWNUM < 6

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Expert Comment

by:dxladner
ID: 22767013
The RowNum clause will get you the first 6 rows of data only. If that is all you are looking for  then use hgassap's example. But using the RowNum will not pull RANDOM sampling throughout the database. You must use the SAMPLE keyword.
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