Compare values of a PHP array with a large table MySQL - php

Question

Ok, normally I would do something like this in PHP if I compared just few values:
// I want to get 1
$a = array(1,2);
$b = array(2);
// It produces 1
$result = array_diff($a, $b);
But in this case, $b is a large table in MySQL with millions of rows and retrieving it to PHP would be crazy, so my DBMS (MySQL) must do the work.
How could I do something like:
-- I need treating $a as a column
SELECT $a NOT IN (SELECT id FROM b);
Example
table B
|id|
2
3
4
array A
array(1, 2, 3, 5);
Result
A - B = A - INTERSECT(A,B) = [1, 5]
Example 2
This is exactly what I need for SQL server. Any ideas to do something similar in MySQL?
Note: A has about 5000 ids, so:
SELECT 1
UNION SELECT 1
UNION SELECT 1
UNION SELECT 2
UNION SELECT 5
...
...produces #1064 - memory exhausted

Answer 1

You can join the variables in the array $a in PHP and use that in your SQL query to retrieve the data, It would efficient in you case.
$in = join(',', array_fill(0, count($a), '?'));
$sql = "
SELECT *
FROM galleries
WHERE id IN ($in)"
Here is a working fiddle to prove that the SQL query will return the desired output.
EDIT :
According your new requirement, You could do the array comparison in
the PHP side because You have to somehow bring up the result from
MySQL to eliminate the result from PHP array. If you retrieve the
array $a from another table then we could have done something like a
join. But in this case we cannot do it. Also you mentioned that the
MySQL table has large number of rows so I assume PHP array will anyway
remove only couple of items from the results after bringing it to the
memory.

Answer 2

If you want to check the values exist or not, you can try this one
<?php
$some_id = "100";
$id = mysql_real_escape_string($some_id); // i use escape to compare IP ADDRESSES. you can remove it
$result = mysql_query("SELECT id FROM your_table WHERE id = '$id'");
if (!mysql_num_rows($result))
{
echo "Not Exists";
}
else
{
echo "Exists";
}
?>
I hope this will help

Answer 3

Consider using the JOIN NULL query:
strSQL = "SELECT t2.id
FROM tableB t1
RIGHT JOIN
(SELECT id
FROM tableB
WHERE id IN (".implode(',',$arrayA).")
) t2
ON t1.id = t2.id
WHERE t1.id IS NULL";
Also, depending on how large $arrayA is, consider appending to temp table and join above, replacing sub query with temp table.