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Hello I am creating a normalized Twitter DB for a project I am working on and wanted a bit of guidance on foreign keys.

I am curious about what the difference would be if for hashtags, symbols, user_mentions, urls and media, I made another field in each table called tweet_ID and the relationship changes to the primary key id in the tweet table to each tables tweet_id? The way I've modelled it means the tweets table has 5 extra fields for each tweet object.

Currently I have the schema designed as follows: Schema 1

Are there glaring issues with the way I have implemented the foreign keys in the model this way?

Thank you!

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So, for each tweet, you can have no more than one hashtag? That doesn't sound right to me.

For tweets and hashtags (and probably for the other four connected tables), I would create a "bridge" table, tweet_hashtag. This table would consist of:

  • tweet_id (foreign key to the tweets table)
  • hashtag_id (foreign key to the hashtagstable)
  • if appropriate, other columns that would apply only to the bridge table, if any (I can't think of any in this case, as I assume a tweet is created at a single moment in time; if tweets could be edited, then a created_on date/time column could be appropriate)
  • (Note: the combination of tweet_id and hashtag_id should be the primary key for this table, as you presumably should only note a given hashtag appears in a given tweet once. You can create a surrogate key (probably just an auto-increment integer or bigint value) if you really want to, or if you do need to be able to have multiple entries of the same hashtag for a single tweet for some reason)

This allows a given hashtag to be associated with many tweets, and a given tweet to have multiple (or no) hashtags.

As noted above, the same probably applies to the other four fields associated with the tweets table (user_mentions, urls, media, symbols).

  • @Adam - glad to help! – RDFozz Sep 7 '18 at 13:46
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Can't judge a schema without seeing the queries that will be run.

Meanwhile, some gut observations...

  • Hardly ever is it necessary to have 40 columns in a table.
  • For scaling social media, counters (a la "Likes") should be in separate tables from the "static" data.
  • Rethink each VARCHAR(45); some look too big, some look too small.
  • What CHARACTER SET will you be using?
  • LONGTEXT and BIGINT are bulky and clumsy. Are you expecting such large values?
  • "link color" is a LONGTEXT?? I would expect ENUM or TINYINT (each only 1 byte) or BINARY(3) holding RGB.
  • statuses_count VARCHAR(45) -- What's up? Is it a single number; if so use a numeric type. If it is a commalist of numbers, then you may be asking for trouble when extracting/updating it.
  • What is indices?? The terminology conflicts with INDEX.
  • What indexes exist on the tables?

One tweet can mention many users, correct? Yet the columns don't support that. The mention table needs id_tweet, not the other way around.

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