Dynamically update sql columns based on number of entries - php

Question

I want to create a table like below:
id| timestamp | neighbour1_id | neighbour1_email | neighbour2_id | neighbour2_email
and so on upto max neighbour 20.
I have two questions:
Should I create columns statically or is there a way to create columns dynamically using php based on the count of json Array?
In either case, how would I refer to the columns dynamically and assign value to them based on jsonArray?
My jsonArray would look something like:
{id:123, email_id:abc, neighbours: [{neighbour1_id:234, neighbour1_email: bcd}, {neighbour2_id:345, neighbour2_email:dsf}, {}, {}...]}
Please advice. Thanks.

Answer 1

It looks like you need to rethink your database structure a bit. To me it looks like you need a single users (or whatever they are) table:
CREATE TABLE `users` (
`id` int(11) unsigned NOT NULL AUTO_INCREMENT,
`email` varchar(255) NOT NULL,
`cretaed_at` timestamp NOT NULL,
PRIMARY KEY (`id`)
);
And another table that defines relations between those users:
CREATE TABLE `neighbors` (
`parent` int(11) unsigned NOT NULL,
`child` int(11) unsigned NOT NULL,
PRIMARY KEY (`parent`,`child`)
);
Now you can add as many neighbors to each user as you want. Fetching them is as easy as:
SELECT * FROM `users`
LEFT JOIN `neighbors` ON `users`.`id` = `neighbors`.`child`
WHERE `neighbors`.`parent` = ?
Where that question mark would become the id of the user from which you are fetching the neighbors, preferably by using a prepared statement.
If it is all JSON you will be working with, and querying isn't much of an issue, you could consider working with a noSql database or document store (like redis or mongoDb), but that is an entirely different story.
Just repeating a bunch of columns x times is definitely not the way to go. Vertical size (# rows) of tables in relational databases is no big issue, they are designed for that. Horizontal size (# columns) however is something to be careful with, as it may make your db uanessacry large, and decrease performance.
Just consider what you would if you want to find a user that has a neighbor with an email address [x]. You would have to repeat your where statement 20 times for each possible email column. And that is just one example...

Answer 2

well, the answer i was working on while pevara was posting theirs faster is almost the same...
CREATE TABLE `neighbours` (
`id` int(10) unsigned NOT NULL AUTO_INCREMENT,
`neighbour_email` char(64) NOT NULL,
PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=0 DEFAULT CHARSET=utf8;
CREATE TABLE `neighbour_email_collections` (
`id` int(10) unsigned NOT NULL,
`email_id` char(64) NOT NULL,
`neighbour_id` int(10) unsigned NOT NULL,
PRIMARY KEY (`id`,`neighbour_id`)
) ENGINE=InnoDB AUTO_INCREMENT=0 DEFAULT CHARSET=utf8;
insert into neighbours values (234, "bcd");
insert into neighbours values (345, "dsf");
insert into neighbour_email_collections values(123, "abc", 234);
insert into neighbour_email_collections values(123, "abc", 345);
select *
from neighbours
left join neighbour_email_collections
on neighbour_email_collections.neighbour_id=neighbours.id
where neighbour_email_collections.id=123;