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I care more about the performance than about NFness. Having a column for each option becomes unwieldy unless such additions are very rare. There is a third option -- the SET datatype allows up to 64 t …

Get rid of user_addresses; instead, have an address_type (varchar) in the addresses table. That also gets rid of the over-normalized "address_types" table. Address_types might be "billing", "mail", " …

In the table Chapter you should have a column book_id. That is the standard way to implement many:1. There no need for an extra table; that is only for many:many.

Perhaps a better policy: When registering a user, store the fee charged into the user's history. Derive the fee from some business logic that may or may not be stored in a database table. Note how …

Turn things around. Table addresses needs a delivery_id. Ditto for the table storage. If you want to avoid having multiple rows for addresses or storages, then have two "many-to-many" tables to map b …

Normalization decreases the hassles; you decide where the cutoff is -- among speed/space/hassle/etc. …

Q1: "correct" in what sense - according to theory or practice or performance? Q2: JOINs are not that deadly. Q3: We need to see the SELECTs that you will use before we can judge your Schema. Q4: …

InnoDB tables really need an explicit PRIMARY KEY. If you don't have a 'natural' key, add an AUTO_INCREMENT. INT(3) and INT(99) mean the same thing -- a 4-byte binary number. Consider changing to T …

To focus on ongoing and future dates... A table with suitable columns for simple cases of repeated actions. One row per repeating event. No specific dates except start and end. A table for excepti …

Which happens more often? Renaming/reordering versus fetching? If you are fetching most of the time, then make that more efficient (PK order), while letting the other be more costly. If you are ren …

Redundant information in a database is a no-no. If you have an index (such as the PRIMARY KEY) on user_id and if there is not thousands of rows for a user, the computing it on the fly is the way to g …

If you are asking about preventing duplicate rows, 'constraining' (user, date) to be "unique" (via UNIQUE KEY or PRIMARY KEY) is sufficient. (See two other answers.) If, on the other hand, you need …

Yes, but at most one can be AUTO_INCREMENT, else they would be fighting over how to number them. No, in the sense that is rarely wise to have two tables instead of one. There are exceptions; what is …

A typical implementation of "multi-tenant" is to have a database for each client. Each database has the same few dozen tables. Security (if you care) is somewhat available at the database level. If y …

Both of these schema anti-patterns have been repeatedly refuted: Do not have multiple 'identical' tables. Do not spread an array across columns. So have one table with lots of rows: sites …