Question

I am new to SQL and I have a basic question about performance.

I want to create a users database which will store information about my users:

• Id
• Log in name
• Password
• Real name

Later I want to perform a SELECT query on: Id, Log in name and Real name.

What would be the best design for this database, what tables and what keys should I create?

Answer 1

If it’s only about those 4 fields it looks like just one table. Primary key on ID, unique index on LoginName. You may not want to store the password, but only a hash.

Depending on your queries, create different indexes. Furthermore, you may not need the ID field at all.

UPDATE:
Creating an index on certain column(s) enables the database to optimize its SQL statements. Given your user table:

USER
    USER_ID BIGINT NOT NULL
    LOGIN_ID VARCHAR(<size>) NOT NULL
    PASSWORD VARCHAR(<size>) NOT NULL
    NAME VARCHAR(<size>) NOT NULL

CONSTRAINT PK_USER PRIMARY KEY ( USER_ID )

The databases I know will automatically create an index on the primary key, which in fact means that the database maintains an optimized lookup table, see WikiPedia for further details.

Now say, you want to query users by LOGIN_ID which is a fairly common use case, I guess, you can create another index like:

CREATE INDEX I_USER_1 ON USER ( LOGIN_ID asc )

The above index will optimize the select * from USER where LOGIN_ID='foo'. Furthermore, you can create a unique index instead, assuming that you do not want duplicate LOGIN_IDs:

CREATE UNIQUE INDEX UI_USER_1 ON USER ( LOGIN_ID asc )

That’s the whole story, so if you want to optimize a query for the users real name (NAME), you just create another index:

CREATE INDEX I_USER_2 ON USER ( NAME asc )