Re: Is this database structure correct? Please help oh wise ones :)

[Rick James]

I have a lot of comments about your schema. Since you want to become a DBA, I will nitpick on the details. (I'm not doing this to be mean; as a DBA, you will need to learn these and many other things.)

car_id int(5) primary key
* Please learn that "(5)" has nothing to do with the range of values for car_id.
* Consider SMALLINT (or other sized int)
* An id is usually UNSIGNED, so state
* PRIMARY KEY should be NOT NULL

year int(4)
* There is a datatype "year"; consider using it instead of INT.
* Again: NOT NULL (presumably)

cost double(5,2)
* That will round to two decimal places on input, then convert to binary, thereby leading to future roundoff problems. Suggest DECIMAL(5,2) instead.

name varchar(20)
* Character set? These days, utf8 is "thinking globally"
* Then, utf8_unicode_ci is 'better'.
* I'll bet you have encountered names longer than 20 characters.
* Perhaps you will need to look up a buyer by his name?

tel int(10)
* This time the misinterpretation of "(10)" will lead to a bug.
* Think globally.

origin varchar(15)
* What is "origin" about? (A COMMENT would have helped.)

Missing fields?
* When (eg, when was repair made)
* Who (eg, who entered the data; who repaired; etc)
* Where (...)

What SELECTs will be done against this schema? Given them, we can discuss whether you need more indexes.

Since you mention FOREIGN KEYs, I assume you will be using InnoDB?

Come back with SHOW CREATE TABLE for each, and I may see more details to critique.

Good luck.