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SQL Weaknesses on Database Processing

SQL Weaknesses on Database ProcessingSQL Weaknesses on Database Processing (book)

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This book describes some interesting aspects of the weaknesses and conflictive aspects that the language SQL has in Database Processing, it includes some characteristics of the language that are valid from the perspective of the mathematical theory of Logic, but in the queries could lead us to misinterpretations of results. The intent of this book is to be used along with SQL books because it focuses specifically on the weaknesses and conflictive aspects of the language SQL. This work is an essential resource for any IT professional who works with SQL databases, because the quality of the information in a SQL database depends entirely on the quality of the database queries, for this reason is essential to know the weaknesses and conflictive aspects of the SQL language to build correct queries. It’s assumed that the reader has an intermediate knowledge of the language SQL.
You can find some SQL weaknesses examples on my Blog: http://dbtips.wordpress.com/
and its videoclip in youtube.com: http://www.youtube.com/watch?v=FWrH5K6V6E0/

CONTENTS

This publication consists of the following seven chapters that describes in detail the aspect of the language related to its weaknesses and conflictive characteristics of SQL.

1. “Introduction”:

This has a description of some general aspects of the Database field related to the language SQL, and describes in detail the example Database that is used in the examples of this publication.

2. “The Interpretation of null”

In this chapter we analyze the null mark that SQL has to represent the concept of Missing Information, which can bring us some problems in the interpretation of query result, besides from the fact that there exist some other possibilities of interpretation for this mark in Data Processing.

3. “The Relational Algebra Operations”

In this one you can find an analysis of the lack of equivalency between two possibilities of elaborating queries, one using the Relational Algebra Operations in SQL and the other one using the traditional SQL (i.e. using simple joins).

4. “The conditions EXISTS, IN, ANY and ALL”

In this one we analyze the problems these conditions show when they have elements that include null or the empty set, in such cases the results of the queries can lead us to misinterpretations as it is described in this chapter.

5. “The Aggregation Operators”

This chapter explores the various problems we can have at the time of elaborating queries using the SQL aggregation operators like SUM, AVG, etc., which have a particular behavior when null or the empty set are present.

6. “The Implication”

SQL is based in Logic, that’s why we can build logical expressions like, in this case, the Implication that has a series of aspects that we should consider to avoid errors in interpretations of query formulation.

7. “Operations INSERT, UPDATE and DELETE”

In this chapter we analyze some problems that are found with the SQL operations INSERT, UPDATE and DELETE as a consequence of the problems studied in previous chapters of this publication.