[U2] Unidata Index question

2013-05-23 Thread Jeffrey Butera 

I have two question about how indicies affect queries:

1) If I have an index built for a given field FOO, and perform a query 
with like such as FOO LIKE 'ABC...'  does it benefit from the 
index?  Or is it only queries with equality conditions that benefit from 
the index (eg: FOO EQ 'ABC' )?


2) If I have an index built with Empties=NO and then query with that 
indexed field =, how does it handle the query? Does it not use the 
index at all?


TIA,
Jeff

--
Jeffrey Butera, PhD
Associate Director for Application and Web Services
Information Technology
Hampshire College
413-559-5556

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Re: [U2] Unidata Index question

2013-05-23 Thread Martin Phillips 
Hi Jeff,

1) If I have an index built for a given field FOO, and perform a query 
with like such as FOO LIKE 'ABC...'  does it benefit from the 
index?  Or is it only queries with equality conditions that benefit from 
the index (eg: FOO EQ 'ABC' )?

An index can be used for a LIKE comparison with a literal element at the start 
but not if the ... is at the start.


2) If I have an index built with Empties=NO and then query with that 
indexed field =, how does it handle the query? Does it not use the 
index at all?

Because the condition would be met by a null field and you have disabled 
indexing of null items, the index will not be used.

Beware of queries like
   WITH FLD  4
when using NO.NULLS as again the condition is met by a null item, preventing 
use of an index, whereas
   WITH FLD  4
could use an index.


Martin Phillips
Ladybridge Systems Ltd
17b Coldstream Lane, Hardingstone, Northampton NN4 6DB, England
+44 (0)1604-709200



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Re: [U2] Unidata Index question

2013-05-23 Thread Dave Davis 
For UniData -

FOO LIKE 'ABC'... I think so - because the first part is literal.
FOO LIKE ABC... I don't think so - because you aren't explicitly saying the 
first part is a literal.

-Original Message-
From: u2-users-boun...@listserver.u2ug.org 
[mailto:u2-users-boun...@listserver.u2ug.org] On Behalf Of Jeffrey Butera
Sent: Thursday, May 23, 2013 6:50 AM
To: U2 Users List
Subject: [U2] Unidata Index question

I have two question about how indicies affect queries:

1) If I have an index built for a given field FOO, and perform a query with 
like such as FOO LIKE 'ABC...'  does it benefit from the index?  Or is it 
only queries with equality conditions that benefit from the index (eg: FOO EQ 
'ABC' )?

2) If I have an index built with Empties=NO and then query with that indexed 
field =, how does it handle the query? Does it not use the index at all?

TIA,
Jeff

--
Jeffrey Butera, PhD
Associate Director for Application and Web Services Information Technology 
Hampshire College
413-559-5556

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Dave Davis
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