How to LIMIT a Query which is already been selected? - php

Question

I am trying to LIMIT a Query which is already been selected. I know I can directly do it in my query select, but due to some logics of the code, if I do that way I have to run the query selection twice which (I believe) will increase the computational time!
So, what I am trying is this:
$query1 = $mysqli->query("SELECT * FROM tableName WHERE someconditions");
then, I need to re-select a sub-selection of the $query1 for my Pagination. What I am trying to do is something like this;
$query2 = LIMIT($query1, $limit_bigin, $limit_end);
where $limit_bigin, $limit_end provide the LIMITING range (start and end respectively).
Could someone please let me know how I could do this?
P.S. I know I can do it directly by:
$query1 = $mysqli->query("SELECT * FROM tableName WHERE someconditions");
$query2 = $mysqli->query("SELECT * FROM tableName WHERE someConditions LIMIT $limit_bigin, $limit_end");
But this is running the query twice and slows down the process (I must run the first query without limits due to some logics of the program)
EDIT 1
As per the answers I tried using array_slice in PHP. BUT, since Query is an object it doesn't give the results that was expected. A NULL is resulted form
array_slice($query1, $start, $length, FALSE)

Answer 1

If you have already carried out the query and the result set has been returned to your PHP, you can not then LIMIT it. As you state, then running a second SQL execution of a subpart of the same query is wasteful and repetative.
Don't
Repeat
Yourself.
DRY.
As I said above, repetition causes issues with maintainability as you can easily forget about repetition, tweaking one SQL and forgetting to tweak the other.
Don't
Repeat
Yourself.
DRY.
Use PHP instead
Once you have executed the query, the result set is then passed back to PHP.
So assuming you have a $var with the contents of you SQL query, then you simply need to select the valid rows from the $var, not from the database [again].
You can do this using PHP numerous Array functions. Particularly array_slice().
So;
$query1 = $mysqli->query("SELECT * FROM tableName WHERE someconditions");
Now, to select the second page, say for example rows 10 to 20:
$query2 = array_slice($query1, (10-1), 10 );
This wil then "slice" the part of the array you want. Remember that the array counts will start at zero so to grab row 10 (of an index starting at 1, Typical of a MySQL Auto Increment Primary Key), then you will need to select X number of rows from row (10-1) .
Please also read the manual for PHP array_slice().
Further
As referenced in comments, there is no guarentee that your SQL will return the same values each time in the same order, so it is highly recommended to order your results:
$query1 = $mysqli->query("SELECT * FROM tableName
WHERE someconditions ORDER BY primary_key_column");
Example Data:
$query1 = $mysqli->query("SELECT * FROM tableName WHERE someconditions ORDER BY id");
/***
$query1 = array {
0 => array { 'id' => 1, 'user' => "Jim", 'colour' => "Blue" },
1 => array { 'id' => 2, 'user' => "Bob", 'colour' => "Green" },
2 => array { 'id' => 3, 'user' => "Tom", 'colour' => "Orange" },
3 => array { 'id' => 4, 'user' => "Tim", 'colour' => "Yellow" },
4 => array { 'id' => 5, 'user' => "Lee", 'colour' => "Red" },
5 => array { 'id' => 6, 'user' => "Amy", 'colour' => "Black" }
}
***/
$page = 2;
$size = 3; // number per page.
$start = ($page - 1) * $size; //page number x number per page.
// Select the second page of 3 results.
$query2 = array_slice($query1, $start, $size , FALSE);
/***
$query2 = array {
0 => array { 'id' => 4, 'user' => "Tim", 'colour' => "Yellow" },
1 => array { 'id' => 5, 'user' => "Lee", 'colour' => "Red" },
2 => array { 'id' => 6, 'user' => "Amy", 'colour' => "Black" }
}
***/
You can then use these in a foreach or other standard array manipulation technique.