Possible fallbacks in my pagination technique and how can I improve it? - sql

Question

I want to perform pagination for my web page.The method that I am using (and I found mostly on internet ) is explained below with an example.
Suppose I have the following table user
+----+------+----------+
| id | name | category |
+----+------+----------+
| 1 | a | 1 |
| 2 | b | 2 |
| 3 | c | 2 |
| 4 | d | 3 |
| 5 | e | 1 |
| 6 | f | 3 |
| 7 | g | 1 |
| 8 | h | 3 |
| 9 | i | 2 |
| 10 | j | 2 |
| 11 | k | 1 |
| 12 | l | 3 |
| 13 | m | 3 |
| 14 | n | 3 |
| 15 | o | 1 |
| 16 | p | 1 |
| 17 | q | 2 |
| 18 | r | 1 |
| 19 | s | 3 |
| 20 | t | 3 |
| 21 | u | 3 |
| 22 | v | 3 |
| 23 | w | 1 |
| 24 | x | 1 |
| 25 | y | 2 |
| 26 | z | 2 |
+----+------+----------+
And I want to show information about category 3 users with 2 users per page, I am using the following query for this
select * from user where category=3 limit 0,2;
+----+------+----------+
| id | name | category |
+----+------+----------+
| 4 | d | 3 |
| 6 | f | 3 |
+----+------+----------+
and for next two
select * from user where category=3 limit 2,2;
+----+------+----------+
| id | name | category |
+----+------+----------+
| 8 | h | 3 |
| 12 | l | 3 |
+----+------+----------+
and so on.
Now in practice I have around 7000 tuples in a single table.So is there any better way in terms of speed to achieve this or in terms of any fallback this method may have.
Thanks.

Answer 1

You don't want to fetch more values than your current page can handle, so yes, you will essentially be making one query per page. Some other solutions (such as Rails will_paginate) will execute essentially the same queries.
Now, you could build some logic into your client side to do the pagination there - prefetch multiple (or all) pages at once and store them on the client side. This way pagination is handled completely on the client side without need for further queries. It is a bit wasteful if a user is likely to only look at a small percentage of pages overall though.
If your actual production table has more columns in it, you could select only the relevant columns instead of *, or potentially add some sort of order by (for sorting).

Answer 2

I hope this will help, you gotta put your page number in place of your_page_number, and records per page in place of records_per_page which in your sample is 2:
select A.* from
(select #row := #row + 1 as Row_Number, User.* from User
join (select #row := 0) Row_Temp_View
where category = 3
) A
where row_number
between (your_page_number * records_per_page)-records_per_page+1
and your_page_number * records_per_page;
notice that this will fetch you the right records, where your sample will not, and this is because your sample will fetch you always two records, which is not always true, lets say that you have 3 users you wonna show in two pages so your sample will show the first and the second in the first page and it will show the second and the third in the second page which is not right, my code will show you the first and the second in the first page and in the second page it will show you only the third one....

Answer 3

You can use Datatables. It's meant for exact same thing that you are looking for. I successfully use it for paginating more than a million rows, it's very fast & easy to implement.