Using SELECT MAX(Substr( in a subquery to return specific rows

Question

Oracle v10
Here's an example of a query and the output
SELECT ID, SAMPLEID, COMPOUNDNAME, REQUISITION, SUBSTR(REQUISITION,2,4) FROM SEARCH PL1 WHERE SAMPLEID = 'IA 0005 0166';
86907     IA 0005 0166     IA 0005     R2004:001160     2004
98158     IA 0005 0166     IA 0005     R2005:000956     2005I am attempting to only return the newest row of data, in this case the 2005 row.
I tried
SELECT ID, SAMPLEID, COMPOUNDNAME, REQUISITION, SUBSTR(REQUISITION,2,4) FROM SEARCH PL1
WHERE SAMPLEID = 'IA 0005 0166' AND
REQUISITION IN
(SELECT MAX(SUBSTR(REQUISITION,2,4)) FROM SEARCH PL2
WHERE SUBSTR(PL2.REQUISITION,2,4) = SUBSTR(PL1.REQUISITION,2,4));But it returns no results. I feel I am missing something simple.
TIA

Answer 1

Hi,
You're comparing a string to a 4-byte substring from the middle of itself. Those two will never be the same.
Also, I don't think you want the sub-query to be corellated.
Try this:
SELECT      id
,     sampleid
,     compoundname
,     requisition
,     SUBSTR (requisition, 2, 4)
FROM     search      pl1
WHERE     sampleid = 'IA 0005 0166'
AND     SUBSTR (requisition, 2, 4)     -- Changed
     IN  (
             SELECT  MAX (SUBSTR (requisition, 2, 4))
          FROM     search pl2
--           WHERE      SUBSTR (pl2.requisition, 2, 4) = SUBSTR (pl1.requisition, 2, 4)     -- Lose this, maybe
;If different substrings of requisition mean different things, then perhaps they should be stored in different columns. It will be easier to combine the different columns when you want to (e.g., for display) than it will be to split the single string apart every time you need to use only part of it, and it will be much more efficient as well.
If you need to combine them often, you could create a view, or, starting in Oracle 11, use a virtual column.
I hope this answers your question.
If not, post a little sample data (CREATE TABLE and INSERT statements, relevant columns only), and also post the results you want from that data.
Explain, using specific examples, how you get those results from that data.
Edited by: Frank Kulash on Dec 20, 2010 12:59 PM
Formatted code