SQL主键生成

Question

Used SQL Server = MySQL
Programming language = irrelevant, but I stick to Java and C#

I have a theoretical question regarding the best way to go about primary key generation for SQL databases which are then used by another program that I write, (let's assume it is not web-based.)

I know that a primary key must be unique, and I prefer primary keys where I can also immediately tell where they are coming from when I see them, either in my eclipse or windows console when I use a database, as well as in relationship tables. For that reason, I generally create my own primary key as an alphanumeric string unless a specific unique value is available such as an ISBN or SS num. For a table Actors, a primary key could then look like a1, and in a table Movies m1020 (Assuming titles are not unique such as different versions of the movie 'Return to witch Mountain').

So my question then is, how is a primary key best generated (in my program or in the db itself as a procedure)? For such a scheme, is it best to use two columns, one with a constant string such as 'a' for actors and a single running count? (In that case i need to research how to reference a table whose PK spans multiple columns) What is the most professional way of handling such a task?

Thank you for your time.

Answer 1

A best practice is to let your DB engine generate the primary key as an auto-increment NUMBER. Alphanumeric string are not a good way, even if it seems too "abstract" for you. Then, you don't have to worry about your primary key in your program (Java, C#, anything else) ; at each line inserted in your Database, an unique primary key is automatially inserted

By the way, with your solution, I'm not sure you manage the case where two rows are inserted simultaneously... Are you sure in absolutely no case, your primary key can be duplicated ?

Answer 2

Your first line says:-

SQL Server = MySQL

Thats not true. They are different.

how is a primary key best generated (in my program or in the db itself as a procedure)?

Primary keys are generated by MYSQL when you specify the column with primary key constraint on it. The primary keys are automatically generated and they are automatically incremented.

If you want your primary key as alphanumeric(which I personally will not recommend) then you may try like this:-

CREATE TABLE A(
id INT NOT NULL AUTO_INCREMENT,
prefix CHAR(30) NOT NULL,
PRIMARY KEY (id, prefix),

I would recommend you to have Primary key as Integer as that would help you to make your selction a bit easier and optimal.For MyIsam tables you can create a multi-column index and put auto_increment field on secondary column

Answer 3

For MySQL there's a best way - set AUTO_INCREMENT property for your primary key table field. You can get the generated id later with last_insert_id function or it's java or c# analog.

Answer 4

I don't know why you would use "alphanumeric" values - why not just a plain number?

Anyway, use whatever auto-increment functionality is available in whichever DB-system you are using, and stick with that. Do not create primary keys outside of the DB - you can't know when / how two systems might access the DB at the same time, which could cause problems if the two create the same PK value, and attempt to insert it.

Also, in my view, a PK should just be an ID (in a single column) for a specific row, and nothing more - if you need a field indicating that a record concerns data of type "actor" for instance, then that should be a separate field, and have nothing to do with the primary key (why would it?)