From: denevge@my-deja.com Newsgroups: comp.databases.oracle.server Subject: Re: Hypothetical questions Date: Tue, 12 Dec 2000 14:27:38 GMT Organization: Deja.com - Before you buy. Lines: 76 Message-ID: <915ckj$d9u$1@nnrp1.deja.com> References: <9146oh$hko$1@nnrp1.deja.com> NNTP-Posting-Host: 194.7.184.218 X-Article-Creation-Date: Tue Dec 12 14:27:38 2000 GMT X-Http-User-Agent: Mozilla/4.0 (compatible; MSIE 5.0; Windows 98; DigExt) X-Http-Proxy: 1.1 x54.deja.com:80 (Squid/1.1.22) for client 194.7.184.218 X-MyDeja-Info: XMYDJUIDdenevge varchar <-> char the main difference is that varchar has a non-fixed length char has a fixed length When you define a char(20), it always takes 20 bytes. It doesn't matter what is in the field. When you defina a varchar2(20), the number of bytes it takes depends on the data stored in the field. Let's say we put the string "DEJA" in the field, the fields take 4 bytes + length indicator = 5 bytes. It's because of that non-fixed length, that it's possible that doing an update of a varchar2 can cause migration of the row. When updating a varchar2 field, it's possible that the new record doesn't fit in the block no more and it has to be migrated. Hope this helps gert In article , "Michael O'Neill" wrote: > Comments inline > > > 1. BLOBs -- ... If you had the chance to redesign your data model > > from scratch, would you continue to store your BLOBs internally, or > > would you look at storing them outside the database and why? > > It depends. If the data is something that needs to be stored, kept and > retreived for legal reasons now and years down the road, like an Acrobat > .pdf contract - storing as a BFILE may be a very bad idea. Otherwise > storing as a BFILE has always worked out to be the least amount of work for > me. Either or, both the logical and physical model, in my mind would 'look' > the same. What is different is the available access to the data via the > DBMS_LOB package, storage consumption and recovery options, as well as > performance - which all depend on the usage of the data. For store and > forget data, (very little retreival/modification) I have not discovered any > great performance differences. > > > 3) Char vs. Varchar2? I have heard the following arguments for char > > vs. varchar2: > > a) argument 1: You should always use varchar because you save > > space. > > b) argument 2: Use char when all possible values stored in a column > > are about the same length, use varchar when they can have widely > > different lengths. > > c) argument 3: Use char instead of varchar, because varchar can > > cause a row to span multiple blocks, thus taking longer to retrieve > > data. > > > > Which philosophy (a, b, or c, or another different philosophy > > altogether) would you choose when designing a data model and why? > > It depends. Generally #1, though. I don't understand the validity in > stating #2. #3 is not pertinent on whether the data is volitale or not. > For the most part, the person doing the physical data modeling will have > worked through these issues, using their experience. There just isn't any > fixed philosophy to answer your question succinctly. There are simply more > dimensions to consider than the question you ask alone. > > Sent via Deja.com http://www.deja.com/ Before you buy.