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I have an assignment which requires me to design a database.

I have 3 entity types WARD, BED, and BED_ASSIGMENT (which is the "composite" entity type between BED and WARD).

The BED primary key consists of the attributes bed_id and ward_id (each ward has bed number 1 for example, so I need ward_id to properly identify it)

My question is:

I have two attributes: total_bed_ count and total_vacant_bed_count. In which entity type should I place them?

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    You shouldn't have these attributes in any entity. I'm of the strong opinion this shouldn't be stored but queried. – Colin 't Hart Apr 22 at 9:13
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Don't store redundant information. Both total_bed_count and total_vacant_bed_count can be queried.

total_bed_count would be something like select count(*) from bed, while total_vacant_bed_count could be queried if you know which beds don't have patients assigned to them, maybe something like select count(*) from bed where patient is null.

  • thank you Colin – Myaccount Apr 23 at 5:32

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