Question

Need to optimize a query

Asked by: slightwv

I've been staring at this to long and give up.  I might be able to change/create the tables if necessary but I'd rather not.

Using Oracle 10.2.

Given a table of marriage_states (simplified of course):
create table tab1 (husband_state char(2), wife_state char(2));

insert into tab1 values('AL','WA');
insert into tab1 values('AL','NY');
insert into tab1 values('ND','AL');
insert into tab1 values('AL','AL');
insert into tab1 values('AL','AL');
insert into tab1 values('AL','AL');
commit;

What I would like from a single query (it's for a report) is:
- Husbands from AL with wives not from AL
- Wives from AL with husbands not from AL
- Couples where both are from AL

results
----------------------
Husbands 2
Wives 1
Couples 3


Best I can think of now involves 3 full table scans with 2 unions.

select 'Husbands', count(*) from tab1 where husband_state='AL and wife_state != 'AL
union
select 'Wives', count(*) from tab1 where husband_state!='AL and wife_state = 'AL
union
select 'Couples', count(*) from tab1 where husband_state='AL and wife_state = 'AL


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Asked On
2009-06-11 at 16:31:37ID24485100
Tags

database query

,

Oracle SCM

Topics

Enterprise Software

,

Databases Miscellaneous

,

SQL Query Syntax

Participating Experts
2
Points
500
Comments
6

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Answers

 

by: lwadwellPosted on 2009-06-11 at 16:44:32ID: 24607987

Hi slightwv,

try something like ...
SELECT
CASE WHEN husband_state = 'AL' and wife_state = 'AL' THEN 'Couples'
WHEN husband_state = 'AL' THEN 'Husbands'
WHEN wife_state = 'AL' THEN 'Wifes'
ELSE 'Neither'
END as category, count(*)
FROM tab1
GROUP BY
CASE WHEN husband_state = 'AL' and wife_state = 'AL' THEN 'Couples'
WHEN husband_state = 'AL' THEN 'Husbands'
WHEN wife_state = 'AL' THEN 'Wifes'
ELSE 'Neither'
END

lwadwell

 

by: lwadwellPosted on 2009-06-11 at 16:45:54ID: 24607998

slightwv,

If you do not want the 'Either' category ... add
WHERE husband_state = 'AL' or wife_state = 'AL'

lwadwell

 

by: slightwvPosted on 2009-06-11 at 16:50:00ID: 24608021

Thanks for the quick update.  I'll give a try tomorrow when I get back to work but it looks like it just might work.  I knew there had to be an easier way.

 

by: JonasMalmstenPosted on 2009-06-11 at 16:54:53ID: 24608047

I assume you have lots of records in your table, unless you do alot of heavy inserting, consider creating an index

create index idx_tabl_state on tabl(wife_state, husband_state);                        

 

by: slightwvPosted on 2009-06-11 at 17:21:12ID: 24608202

Not a lot of rows by today's standards, 1.5mil and counting but a lot of inserts, no updates and very rare deletes.

I was way ahead of you on indexes if not for the high number of inserts I'm a perfect fit for bitmap indexes.  Regular B-Tree indexes would be skewed to fast and I'd need to many of them.  Remember, I simplified the table a bit.  I have a few of these types of pairs I need to report against.

I'm trying to squeeze the last few seconds out of a 30 second web report and knew there had to be a better way than a 3 way full table scan.  I was just way to deep into the problem and couldn't see the simple path.

If the 'case' select works I'm going to kick myself.  I use them throughout the application in other places.  :(

 

by: slightwvPosted on 2009-06-12 at 06:29:39ID: 31591570

Worked like a charm.

20120131-EE-VQP-002

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