MySQL (exploding/matching array) - php

Question

Question1:
MySQL table
id | array
1 | 1,2,3
2 | 2
3 | 2,3
4 | 4,5,6
$_GET['id'] = 2;
$a = mysql_query("SELECT * FROM `table` WHERE `array` ??? '$_GET[id]'");
In this step, I want to run through the entire array and see if it matches with the $_GET['id'], so it should output:
ids: 1,2,3
Question2:
MySQL table
id | array
1 | 4,5,6
2 | 3,4,7
$_GET['id'] = 4;
$a = mysql_query("SELECT * FROM `table` WHERE `array` ??? '$_GET[id]'");
In this step, I only want to match against the first element in the array, so it should output:
id: 4
I can only think of using PHP to do this, but I'd rather do all that just within the MySQL query, if that is even possible.
$a = mysql_query("SELECT * FROM `table`");
while($b = mysql_fetch_assoc($a))
{
$elements = explode(',', $b['array']);
foreach($elements as $element)
{
if($element == $_GET['id'])
{
echo $b['id'].'<br />';
}
}
}
or
$a = mysql_query("SELECT * FROM `table`");
while($b = mysql_fetch_assoc($a))
{
$array = $b['array'];
if(in_array($_GET['id'], $array))
{
echo $b['id'].'<br />';
}
}
that would look just awful.

Answer 1

That you can/should structure your database differently has already been mentioned (see http://en.wikipedia.org/wiki/Database_normalization). But....
See FIND_IN_SET()
mysql> SELECT FIND_IN_SET('b','a,b,c,d');
-> 2
e.g.
<?php
$mysql = init();
bar($mysql, 1);
bar($mysql, 2);
bar($mysql, 3);
bar($mysql, 4);
function bar($mysql, $x) {
$sql_x = mysql_real_escape_string($x, $mysql);
$result = mysql_query("SELECT id, foo FROM soTest WHERE FIND_IN_SET('$sql_x', foo)", $mysql) or die(mysql_error());
echo "$x:\n";
while( false!==($row=mysql_fetch_array($result, MYSQL_ASSOC)) ) {
echo $row['id'], ' ', $row['foo'], "\n";
}
echo "----\n";
}
function init() {
$mysql = mysql_connect('localhost', 'localonly', 'localonly') or die(mysql_error());
mysql_select_db('test', $mysql) or die(mysql_error());
mysql_query('CREATE TEMPORARY TABLE soTest (id int auto_increment, foo varchar(64), primary key(id))', $mysql) or die(__LINE__.' '.mysql_error());
mysql_query("INSERT INTO soTest (foo) VALUES ('1,2,3'), ('2,4'), ('3'), ('2,3'), ('1,2')", $mysql) or die(__LINE__.' '.mysql_error());
return $mysql;
}
prints
1:
1 1,2,3
5 1,2
----
2:
1 1,2,3
2 2,4
4 2,3
5 1,2
----
3:
1 1,2,3
3 3
4 2,3
----
4:
2 2,4
----
MySQL can't use indices to perform this search, i.e. the query results in a full table scan, see Optimizing Queries with EXPLAIN
edit:
For your second question you only have to change the WHERE-clause to
WHERE FIND_IN_SET('$sql_x', foo)=1

Answer 2

Your data structure in the DB is not optimal for querying the way you want it.
For the first question:
mysql_query("SELECT * FROM table WHERE array LIKE '%,$_GET[id],%' OR array LIKE '$_GET[id],%' OR array LIKE '%,$_GET[id]' OR array = '$_GET[id]'");
For the second:
mysql_query("SELECT id, SUBSTR(array, 1, POSITION(',' IN array) - 1) AS array FROM table WHERE array LIKE '$_GET[id],%' OR array = '$_GET[id]'");
As you can see, these queries aren't pretty, but they'll do what you want.

Answer 3

Untested, but you should be able to use:
Question 1:
SELECT * FROM table WHERE array REGEXP '(^|,)?(,|$)';
// Match either the start of the string, or a , then the query value, then either a , or the end of the string
Question 2:
SELECT * FROM table WHERE array REGEXP '^?(,|$)';
// Match the start of the string, then the query value, then either a , or the end of the string
Where ? is replaced with your $_GET value.
No idea on the performance of this.

Answer 4

I'd recommend you to bring your database to the first normal form, e. g.
CREATE TABLE t_master (
id INT PRIMARY KEY AUTO_INCREMENT
);
CREATE TABLE t_array (
id INT PRIMARY KEY AUTO_INCREMENT,
master_id INT NOT NULL,
value INT,
CONSTRAINT fk_array_master_id FOREIGN KEY (master_id) REFERENCES t_master (id)
);
Then you can find records in t_master that have a specific value with
$q = 'SELECT m.* ' .
'FROM t_master AS m INNER JOIN t_array AS a ON a.master_id = m.id ' .
"WHERE a.value = '" . mysql_real_escape_string($_GET['id'], $db) . "' " .
'GROUP BY m.id';
The most important advantage is that if you have a lot of values, you can add an index to find them much faster:
ALTER TABLE t_array ADD INDEX idx_value (value);
A less evident, but not the last advantage is that your queries become more logical and structured.

Answer 5

If you can't normalise your schema (which is the best option:
SELECT *
FROM table
WHERE ','+array+',' LIKE '%,$_GET[id],%'
But if you need to access the records by id, then you really should normalise

Answer 6

First One:
SELECT * FROM table WHERE array LIKE '$_GET[id],%' OR array LIKE '%,$_GET[id],%' OR array LIKE '%,$_GET[id]' OR array = '$_GET[id]
Second One:
SELECT * FROM table WHERE array LIKE '$_GET[id],%' OR array = '$_GET[id]
Explanation:
'$_GET[id],%' will match, if array is start with $_GET[id]
'%,$_GET[id],%' will match, if $_GET[id] is between any two of array items
'%,$_GET[id]' will match, if array is end with $_GET[id]
array = '$_GET[id]' match, if the array contains only one item equal to $_GET[id]