Thread
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Antw: many-many mapping between unique tables
Gerhard Dieringer <dieringg@eba-haus.de> — 2000-10-16T06:57:52Z
>>> Indraneel Majumdar <indraneel@www.cdfd.org.in> 16.10.2000 20.11 Uhr >>> > Hi, > > I am facing a problem in mapping between two tables containing unique > entries > > T1 T2 > _________ ________ > | x1 | | y1 | > | x2 | | y2 | > | x3 | | y3 | > --------- --------- > > x(i) points to 1 or more entries in T2. y(i) points to one or more entries > in T1. How do I store this mapping? I'd cannot use an array due to size > restrictions and inability to extract data easily for furthur processing. > > I don't want to put everything into a single table and repeat values in > the 2nd column since these are really huge tables and I cannot increase > overhead by increasing data redundancy. > > Is there some way to do something about this? > > \Indraneel > > /************************************************************************. > # Indraneel Majumdar ¡ E-mail: indraneel@123india.com # > # Bioinformatics Unit (EMBNET node), ¡ URL: http://scorpius.iwarp.com # > # Centre for DNA Fingerprinting and Diagnostics, # > # Hyderabad, India - 500076 # > `************************************************************************/ I'm not sure if I understand your question. Is it right, that the x(i) are different values of an column x in table T1 and the y(i) are different values of an column y in table T2? And you want to have a n:m relation between the two tables? Then you need a third table T12 with columns x and y, that contains one row for each mapping of a x(i) with a y(j). I hope this helps. Gerhard
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Re: JDBC Performance
Josh Berkus <josh@agliodbs.com> — 2000-10-16T15:13:56Z
Mr. May, For discussions of JDBC, please subscribe to the pgsql-interfaces list. You will find many JDBC users on that list. -Josh Berkus P.S. PGSQL folks, is there any way we can clarify this on the web page? The JDBC users seem to keep ending up on this list. -- ______AGLIO DATABASE SOLUTIONS___________________________ Josh Berkus Complete information technology josh@agliodbs.com and data management solutions (415) 436-9166 for law firms, small businesses fax 436-0137 and non-profit organizations. pager 338-4078 San Francisco -
Re: Antw: many-many mapping between unique tables
KuroiNeko <evpopkov@carrier.kiev.ua> — 2000-10-16T15:14:27Z
> > I am facing a problem in mapping between two tables containing unique > > entries > > > Then you need a third table T12 with columns x and y, that contains one > row for each > mapping of a x(i) with a y(j). That's it. Normalize it. Relation T12 may also require the third field, `direction', to specify whether this is T1 -> T2 or T2 -> T1. In general, it'd be much better to re-design data layout. -- Well I tried to be meek And I have tried to be mild But I spat like a woman And I sulked like a child I have lived behind the walls That have made me alone Striven for peace Which I never have known Dire Straits, Brothers In Arms, The Man's Too Strong (Knopfler)
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JDBC Performance
Craig May <craig.may@s2.enthdimension.com.au> — 2000-10-16T19:49:50Z
Hi, I've been using the postgresql.Driver with JDBC for some time. Initially, I was passing Statement objects through functions to each of the Classes. This was working beautifully. I have since adapted my application to support MS SQL Server. SQL Server doesn't allow a statement object to perform multiple queries, so i have changed the application to create additional Connections. This has reduced it's performance around 400%. I'm using the driver contained with Postgresql 7.1 Does anyone have ideas on increasing performance with multiple connections? Kind Regards, Craig May Enth Dimension http://www.enthdimension.com.au
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Re: Antw: many-many mapping between unique tables
Indraneel Majumdar <indraneel@www.cdfd.org.in> — 2000-10-16T20:13:56Z
Yeah you understand the problem perfectly. The third table will definitely contain unique entries if you take both x and y simultaneously. I wanted some way of mapping where I would not need to repeat individual values of x and y. I am not from a maths background and have absolutely no idea of database design. Is it possible to map the columns without repeating values? \Indraneel On Mon, 16 Oct 2000, Gerhard Dieringer wrote: > I'm not sure if I understand your question. Is it right, that the x(i) are different values > of an column x in table T1 and the y(i) are different values of an column y in table T2? > And you want to have a n:m relation between the two tables? > Then you need a third table T12 with columns x and y, that contains one row for each > mapping of a x(i) with a y(j). > > I hope this helps. > > > Gerhard /************************************************************************. # Indraneel Majumdar ¡ E-mail: indraneel@123india.com # # Bioinformatics Unit (EMBNET node), ¡ URL: http://scorpius.iwarp.com # # Centre for DNA Fingerprinting and Diagnostics, # # Hyderabad, India - 500076 # `************************************************************************/
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Re: JDBC Performance
Peter Mount <peter@retep.org.uk> — 2000-10-17T19:23:17Z
On Mon, 16 Oct 2000, Josh Berkus wrote: > Mr. May, > > For discussions of JDBC, please subscribe to the pgsql-interfaces > list. You will find many JDBC users on that list. > > -Josh Berkus > > P.S. PGSQL folks, is there any way we can clarify this on the web page? > The JDBC users seem to keep ending up on this list. I think it needs to be mentioned somewhere on the postgresql site. I've had this on my site for the last 3 years ;-) Also, I only get the sql & general lists here at home (retep.org.uk), but get interfaces at work as well so I can sometimes answer it faster if it's posted to interfaces. Peter -- Peter T Mount peter@retep.org.uk http://www.retep.org.uk PostgreSQL JDBC Driver http://www.retep.org.uk/postgres/ Java PDF Generator http://www.retep.org.uk/pdf/