help with clarifying the correct way to index data in a database

Hello everyone,

sorry to bother everyone , but i am still new to databases and indexing and i am trying to build my first CMS system.

i am building a database system in which members will be able to communiate with each other via sent messages sent. The messages will be stored in a database and members will be able to retrieve the messages via a sql commands .

this is the sql command for the creation of the database table

[php]

CREATE TABLE massages(

receiver_id int(11) NOT NULL ,
sender_id int(11) NOT NULL ,
messages varchar(255) NOT NULL,
date_sent varchar(255) NOT NULL,
receiver_memtype varchar(30) NOT NULL,

INDEX massage (receiver_id)

);

[/php]

my question now is this;

is the index i have used correct and also the best way to way to access the messages .
i anticipate having millions of messages, so i will obviously need to be able to acess them quickly.

should i index it the following way

INDEX massage (receiver_id, sender_id )

Also, i am not sure how to do the sql command so that messages will follow on from each other. i.e if a user respond to a message,how do i get the messages to follow on from each other. i.e should the messages each have a seperate Id number.

warm regards

andreea

The index depends,
it’s used to identify rows, you can use what you want,

but y think you are looking an answer for the KEYs, it will be UNIQUE,

a person can receive 2 (or more) massages from the same sender?
if the answer are Yes, PRIMARY KEY must be other field that there are not at this schema
If the answer ar NO, PRIMARY KEY must be receiver, sender :

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