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Retired. Once a programmer, then a DBA.


8h
comment One field with multiple values?
Can a driver have more than one truck?
2d
answered Database with only text fields
Oct
19
comment Applying normalization to a relational Database (Access & SQL Server)
You need to supply more information if you want help determining what NF each of your tables are in. In particular, an analysis of the subject matter should reveal "functional dependencies" between groups of data items. For example, "ZIP" is dependent on GuestID, but not on GuestName, because two different guests could have the same name. FDs are features of the subject matter itself, and NOT of design choices. Some FDs may be obvious to us, based on what "everybody knows" about hotels. But some are not obvious at all, and you have to say what they are.
Oct
19
comment Why does a UNIQUE constraint allow only one NULL?
This is getting to be a philosophical discussion. I'm signing off.
Oct
18
comment Why does a UNIQUE constraint allow only one NULL?
@supercat in that case, let's have two different keywords, instead of overloading NULL. NULL should continue to mean "no value present" as it does now. Choose some other keyword for "value exists, but not provided" or whatever else.
Oct
18
comment Why does a UNIQUE constraint allow only one NULL?
@JoelBrown in addition, there is NULL(unavailable). This is ambiguous as to whether a value exists, but was not supplied, or no value even exists, or "don't know", or "don't care". This is really the only "meaning" that can always be attached to NULL. Any inferences beyond that are a matter of previously agreed convention, or deductive reasoning, like the curious incident of the dog in the night.
Oct
18
answered How is SQL used from an end-user perspective?
Oct
18
comment How is SQL used from an end-user perspective?
Is the secretary of a company the secretary of the boss of the company? Many tasks that used to be performed by a personal secretary are now done by the boss directly. Among these are typing, filing, call screening, to do list management, schedule management and so on.
Oct
17
comment Can't finish my ER diagram
You have to distinguish between poor design and poor analysis. Poor design involves setting up the wrong tables with the wrong components and rules. Poor analysis involves a misunderstanding of the underlying subject matter. Library science is a well established field, and the librarians know an awful lot about it, even in the face of today's rapid changes. These are your subject matter experts, not some whiz bang database designers. Good luck with the search.
Oct
17
answered Can't finish my ER diagram
Oct
16
revised A question regarding the performance of normalization
typo
Oct
16
comment A question regarding the performance of normalization
Thank you. Accepting an answer is sufficient.
Oct
15
answered A question regarding the performance of normalization
Oct
11
comment Does the creation of constraints affect the views that have been created earlier?
Most database systems forbid updates through views that join tables together, as in this case.
Oct
11
comment Does the creation of constraints affect the views that have been created earlier?
For most database systems, the existing data will be checked at the time the new constraint is added. If any existing data violates the constraint, the new constraint will not be added.
Oct
9
revised erd wiki description
copied tag wiki from SO.
Oct
9
answered What would the relational diagram look like in this situation?
Oct
9
comment What would the relational diagram look like in this situation?
Thanks for the wikipedia reference. Yes, we learned it differently. The main issue here is what's of most use to the questioner and future visitors.
Oct
9
suggested suggested edit on erd tag wiki
Oct
7
comment What would the relational diagram look like in this situation?
What's relevant for the OP is how the teacher divides up the layers.