How to retrieve samples from the database ?
Suppose I have many tagged entities (e.g. blog posts with tags) to store
in an SQL database. For example:
post1: work
post2: work, programming, java, work
post3: work, programming, sql
post4: vacation, photo
post5: vacation
post6: photo
Suppose also I have a list of tags
work, vacation
Now I'd like a sample: two posts with tags from the list. For example
sample1: post1 and post2
sample2: post1 and post4
sample3: post2 and post5
In addition I'd like the sample to contain all tags in the list. Note that
sample1 does not meet this requirement since the set of tags of the sample
entities does not contain tag vacation from the list.
I would like also all tags occurrences to be equal. Let's consider 2
samples of size 4.
sample1: post1, post2, post3, post6
sample2: post1, post3, post4, post5
Note that sample1 does not meet this requirement since tag work occurs 3
times in it and vacation occurs only once.
My question is: how to design a relational database and SQL query to
retrieve samples of given size?
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