akk kur akk kur - 1 year ago 86
SQL Question

Storing chat messages inside a MySql table

For the last couple of weeks I've been working on a web based chat client application and I have a question regarding storing chat messages inside a MySql table. I created a table called conversations and for now it consists of 5 fields;

user1ID, user2ID ,messages(mediumtext), status, timestamp.

When I test the chat application everything works perfectly fine, but the problem is every time a user sends something, I'm appending that value into my 'messages' field as a new line. And when it comes to retrieving the message, my sql code reads the whole thing and show it to the corresponding user. So the amount of data linearly increase by the amount of text added into the messages field.
My question is, is there any way to SELECT only the last line from a text field or maybe another solution that will reduce the amount of transferred data.

Answer Source

You need a better db schema - more relational. Doing so will give you some other improvements as well (password protected chats and multi-user chat to name a couple)

Here is one take on an ERD for your db.

enter image description here

5/6/2016 edit Adding DDL with (hopefully) improved field types and names

    user_id CHAR(32),
    user_login VARCHAR(255),
    user_password CHAR(64),
    user_email VARCHAR(400),
    PRIMARY KEY (user_id)

    message_id CHAR(32),
    message_datetime DATETIME,
    message_text TEXT,
    message_chat_id CHAR(32),
    message_user_id CHAR(32),
    PRIMARY KEY (message_id)

CREATE TABLE user_chat
    user_chat_chat_id CHAR(32),
    user_chat_user_id CHAR(32),
    PRIMARY KEY (user_chat_chat_id,user_chat_user_id)

    chat_id CHAR(32),
    chat_topic VARCHAR(32),
    chat_password CHAR(64),
    user_chat_user_id CHAR(32),
    PRIMARY KEY (chat_id)

CREATE INDEX user_login_idx ON user (user_login);
ALTER TABLE message ADD FOREIGN KEY message_chat_id_idxfk (message_chat_id) REFERENCES chat (chat_id);

ALTER TABLE message ADD FOREIGN KEY message_user_id_idxfk (message_user_id) REFERENCES user (user_id);

ALTER TABLE user_chat ADD FOREIGN KEY user_chat_user_id_idxfk (user_chat_user_id) REFERENCES user (user_id);

ALTER TABLE chat ADD FOREIGN KEY chat_id_idxfk (chat_id,user_chat_user_id) REFERENCES user_chat (user_chat_chat_id,user_chat_user_id);