Question

regexp

Asked by: it-rex

I have to huge tables I want to show similar colums between them so far the best way is
to use
regexp ;
the problem is the 2 tables have no relationship like Pk fK it does not exist and they are both very huge
right now we are doing

select * f rom first_table t1,second_table  t2
where regexp_like (t1.name,t2.provname,'i');

but this is taking way too long and it seems like it will create a cartisian product;
any ideas how to improve this or bettter join it?

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Asked On
2009-10-16 at 08:37:13ID24818436
Tags

regexp

Topics

Oracle 10.x

,

Oracle Database

Participating Experts
5
Points
500
Comments
9

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Answers

 

by: paquicubaPosted on 2009-10-16 at 10:29:16ID: 25591518

If you don't have a join key, then all you can do is to use t1.name & t2.provname. I would use the regular LIKE operator (faster) in your case, unless you're doing somthing fancy.

Try using PARALLEL hint...

Good Luck!

 

 

by: flow01Posted on 2009-10-16 at 11:12:36ID: 25591893

do I interprete regexp_like (t1.name,t2.provname,'i') as
that you want comparing the to columns case-insenstive ?

In that case you could also use
where UPPER(t1.name) = UPPER(t2.provname);

You would stil have your cartesian product.

1 step further would be to define a function based index  
with column UPPER(name)  on t1
or
with column UPPER(provname) on t2
That wil  cost time to create and diskspace to store,
but after computing statistics the full-table access on both tables should be replace by
1 full table and 1 new-index access.

You can also create both indexes and let Oracle seek out the best approach.

 

by: it-rexPosted on 2009-10-16 at 11:20:10ID: 25591965

thanks flow01:
paquicuba: but how to use the like operator in this case between 2 columns?

 

by: sventhanPosted on 2009-10-16 at 11:45:14ID: 25592193

@ it_rex

Is your table partitioned? How long does it take to compare?  How many rows/columns in the table? Do you have index?

 

by: gatorvipPosted on 2009-10-16 at 12:02:11ID: 25592336

another suggestion would be to create indexes on the length of each field (assuming they are varchar2 type) and then doing a prefilter for only those fields that correspond in length. For example (also using paquicuba's suggestion to use LIKE)

select * from 
(
select t1.name, lower(t1.name) name_low, t2.provname, lower(t2.provname) provname_low
from
first_table t1,second_table  t2
where length(t1.name)>=length(t2.provname)
)
where name_low like '%'||provname_low||'%'

                                              
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Select allOpen in new window

 

by: it-rexPosted on 2009-10-16 at 12:53:18ID: 25592758

sventhan:
the table is not partioned
it is almost 7 million rows;we do have indexes regular and domain;
but it is a fact that regexp can not use any indexes

 

by: it-rexPosted on 2009-10-16 at 12:56:40ID: 25592788

experts just ignore the case sensitive issue ;
what i am wondering about is .
is not it common with ETL process to try to append data came from a different data store;
in which case you will have no relationship betwen the new data and your current data like no pk fk relationship;
in a case that you need to check the names and say some names are misspelled or look some how different what is the best tech in this case?

 

by: mrjoltcolaPosted on 2009-10-17 at 05:29:15ID: 25595750

You are in the realm of Data Mining and custom ETL code now. Probably time to get a coder involved.

 

by: it-rexPosted on 2009-10-18 at 20:07:07ID: 31642157

thanks all

20120131-EE-VQP-002

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