Question

I have two tables, a main one, and one that supports the main table, very very similar to what wordpress has, posts and posts_meta.

Main table:

id
title,
content

id  | title     | content
1   | one       | content one
2   | two       | content two

Meta table:

id
item_id
key
value

id  | item_id   | key       | value
1   | 1         | template  | single
2   | 1         | group     | top
1   | 2         | template  | page
2   | 2         | group     | bottom

And my goal is, in the end, have an array with the data from the main table, merged with the meta table. example:

$data = array(
    array(
        'id' => 1,
        'title' => 'one',
        'content' => 'content one',
        'template' => 'single',
        'group' => 'top'
    ),
    array(
        'id' => 2,
        'title' => 'two',
        'content' => 'content two',
        'template' => 'page',
        'group' => 'bottom'
    )
);

What is the best way to achieve this in a way that preforms good?

I am using PDO to connect to my database, and how Im doing right now is, I first query the data on the first table, and then for each result, i query the meta table, I use prepared statements for this, since it’s suposed to be fast, but even so, it’s harming the performance of my script.

Thank you

Answer 1

Instead of querying meta table for each result from first query

you should extract the ids from the first result:

$rows = q('SELECT * FROM posts');
$byIds = [];
foreach ($rows as &$row)
{
    $byIds[$row['id']] =& $row;
}

and run second query:

$rows2 = q('SELECT * FROM posts_meta WHERE item_id IN (' . implode(',', array_keys($byIds)) . ')');

Then loop the results in PHP and merge with first query results.

foreach ($rows2 as $row2)
{
    $byIds[$row2['item_id']][$row2['key']] = $row2['value'];
}

You have your merged results in $rows variable now:

var_dump($rows);

This way you will have only 2 db requests.

Please note that i have used $byIds as array of references so i dont have to search row with specific id in second loop. This way order of elements in $rows are preserved.