Sunday, June 26, 2022

Repeating Groups and 1NF (T&N)

“A commonly used example of a table that is not in 2-NF is one with repeated attributes (i.e. child1, child2, child3). However, after examining the definition of 2NF in your book PRACTICAL ISSUES IN DATABASE MANAGEMENT, it seems to me that tables such as these do in fact satisfy 2NF. Am I missing something?” --Reader

Saturday, June 11, 2022

SMS: Order and Relational Databases

Note: In "Setting Matters Straight" I post on LinkedIn online Q&As that involve fundamentals under the header "What's Right and Wrong with this Database Picture" and then debunk them here. The purpose is to induce practitioners to test their foundation knowledge against our debunking, where we explain what is correct and what is fallacious. For in-depth treatments check out the POSTS and our PAPERS, LINKS and BOOKS (or organize one of our on-site/online SEMINARS, which can be customized to specific needs). Questions and comments are welcome here and on LinkedIn.

Q: “I'm not sure what this means: "The order of the rows and columns is immaterial to the DBMS?" -- could anyone explain?”

A: “It means two things:
The engine is under no obligation to insert new rows immediately following the previously inserted row(s)... During processing of selects, the optimizer is free to use any index it finds efficient to use or none at all... For this reason, if the order of returned data is important to your processing, then you must include an ORDER BY clause.”

Q: “How do you reorder fields in the database?”

A: “Depends on how you define "reorder". What view of your data are you trying to set the order. Are you in Table Design view? ... Are you looking at form? The answer is different depending on what you are referring to.”
--Quora.com
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