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Glad to be of help
It is a big subject but some problems with SQL databases are.

1. Duplicates. In a relational database, all data is stored as relations. As a relation is a set it is a logical absurdity for it to contain duplicates from a mathematical point of view. As soon as you issue a query without the primary key in, you generally get something that isn't a relation anymore in an SQL database. This causes all sorts of problems with both closure and with performance, consider if a relation (or table in SQL terms) contains a million rows and we select a single column from that table that only contains the same value in half the rows.

2. Violation of closure. As the result of every relational operator should be another relation this means that in theory you can nest relation operators infinately. However to achieve this with SQL you generally have to resort to procedural methods or temporary tables. I believe the latest SQL standard does implement sub queries in the FROM clause which is a step in the right direction, but I don't know if any vendor has implemented this yet. However the whole duplicates problem rears its ugly head again here too.

3. Logical/Physical Independence. The logical view in an SQL database is far too close to the physical representation. In general when tuning SQL you run the continual risk of inadvertantly changing your logical intentions, with all the inherent risks. The whole point of the relational model is that it is a logical model and vendors are then free to implement it from a physical perspective however they wish. However end users and application programmers should not need to know about the physical implementation.

I could go on but instead I recommend Chris Date's Introduction to Database Systems. A classic work on the subject.
Posted by: jorwell   Posted on: 04/14/04 You are currently: a Guest | Members login | Terms of Use
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Disappointing  jorwell | 04/14/04
Read it and weep  Expatriate US Geek | 04/14/04
But my objection is...  jorwell | 04/14/04
Could you be more specific?  Not average Joe | 04/14/04
Glad to be of help  jorwell | 04/14/04
Mmmmm  Not average Joe | 04/14/04
I still think you should read further  jorwell | 04/14/04
Your objection 2 doesn't make sense  jorwell | 04/15/04
In response to #2  nbuwalda | 04/15/04
Good old IBM  jorwell | 04/15/04
not relational  dlevesqu | 04/14/04
Good to hear  jorwell | 04/15/04
"This is the sort of pedantic nonsense ..."  escoles@... | 04/15/04
We are talking about mathematics here  jorwell | 04/15/04
I know you're talking about math  escoles@... | 04/15/04
A mathematical theory is "arbitrary criteria"?  jorwell | 04/15/04
inconsistent results  NemesisNL | 04/16/04
Thank you for your comment  jorwell | 04/16/04
Not ready for prime time  StorageGuru | 04/14/04
Re: Not ready for prime time  ma.rk | 04/14/04
Oracle also isn't relational  jorwell | 04/14/04
I'm curious...  Yen_z | 04/14/04
Regretably none at present  jorwell | 04/14/04
Don't tell my customers  Chad_z | 04/14/04
A question  jorwell | 04/14/04
Nonsense question  NemesisNL | 04/14/04
Dude, you need to calm down  ma.rk | 04/14/04
"It all has its place": Amen. [nt]  escoles@... | 04/15/04
Not ready for prime time?  FederalistPaperBoy | 04/14/04
for which it's suited  SC-man | 04/16/04
I strongly disagree  nycran | 02/17/05
Works great for us.  issthatso | 04/14/04
Not going to be a factor...  Mike Cox | 04/14/04
Oh dear...  jorwell | 04/14/04
Ah, satire and irony  Expatriate US Geek | 04/14/04
Give it a rest, Mike. Please.  AtypicalZork | 04/14/04
Give it a rest, Mike. Please.  SC-man | 04/16/04
SQL-92 has been replaced with...  B.O.F.H. | 04/14/04
Someone needs to  ma.rk | 04/14/04
What's SQL Server?  Linux_Developer | 04/14/04
You'd be more grateful than that  StorageGuru | 04/15/04
Wow, this was really a success!  Linux_Developer | 04/16/04
Hopefully doesn't take cue on security  Xunil_Sierutuf | 04/14/04
SQL Servers Great - But Alternatives are out there  bhafner | 04/14/04
If only...  No_Ax_to_Grind | 04/14/04
Re: if only  B.O.F.H. | 04/14/04
You know...  No_Ax_to_Grind | 04/14/04
He was sayig that OSS can be better than "good enough"  j.m.galvin | 04/14/04
Thank you so much for the intrepretation.  No_Ax_to_Grind | 04/14/04
RE: THank you..  Iain_Peters | 04/14/04
bitty is right --nobody is surprised he couldn't make the connection.  Spam-ZD | 04/14/04
Perhaps this is a fialure to Bitty...  B.O.F.H. | 04/14/04
Reality check  Chad_z | 04/14/04
Did you read the article?  No_Ax_to_Grind | 04/14/04
Ouch  NemesisNL | 04/14/04
Which CEO and which company are you referring?  B.O.F.H. | 04/14/04
Codd and SQL  jorwell | 04/14/04
Not really a problem  Patrick Jones | 04/14/04
Not really Patrick  No_Ax_to_Grind | 04/14/04
MySQL is no more for the desktop than SQL Server or Oracle  B.O.F.H. | 04/14/04
True, that's why the CEO said...  No_Ax_to_Grind | 04/14/04
e-commerce sites are minimal needs?  B.O.F.H. | 04/14/04
Once more, what did the CEO say?  No_Ax_to_Grind | 04/14/04
I suspect that you need to move beyond the desktop!  B.O.F.H. | 04/14/04
The real problem is apples v. oranges  escoles@... | 04/15/04
Ok  NemesisNL | 04/14/04
By your logic, then, SQL Server is for those with minimal needs...  escoles@... | 04/15/04
That is where we differ  Patrick Jones | 04/14/04
Beating microsoft at their own game  boxmonkey | 04/14/04
I don't know about that one ...  coffeenite | 04/14/04
well  boxmonkey | 04/14/04
It's a question of which end of the wire does the work  StorageGuru | 04/15/04
What complete and utter garbage  Takalok | 04/14/04
Information direct from...  jorwell | 04/14/04
So you learned to read.  Snippy Clippit | 04/14/04
This isn't a competition  jorwell | 04/14/04
You've misjudged your audience, big boy...  Snippy Clippit | 04/15/04
You can't answer my arguments...  jorwell | 04/15/04
Back the truck uo  ShadeTree | 04/14/04
It easily verifiable  j.m.galvin | 04/14/04
I never questioned...  ShadeTree | 04/15/04
Linux is the cheap choice  StorageGuru | 04/15/04
Absolutely no perspective  nycran | 02/17/05
Vaman DataServer beats MySQL every way  Dev Mehta | 04/15/04

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