SQL query taking too long to execute - php

Question

I am currently working on a project that requires me to scan the Public Whip Raw Data and return a list of MP's names (who have voted for a policy that matches the keywords that have been input, eg "fox hunting). The current SQL query takes about 30 seconds to finish executing, which is way too long.
This is the SQL query that looks in the "distance" table and the "policy" table. (This is what is taking too long to execute)
$sql = "SELECT DISTINCT distance.mp_id from distance WHERE distance.distance < 0.2 AND distance.dream_id IN (SELECT dream_id from policy WHERE UPPER(policy.title) LIKE UPPER('%".$keyword."%')) ORDER BY distance.distance LIMIT 5";
This is the rest of the code that just echo's out the mp names
$results = mysql_query($sql);
echo "<ul>";
while ($row = mysql_fetch_array($results)) {
$mpid = $row['mp_id'];
$sql = "SELECT mp.first_name,mp.last_name FROM mp WHERE mp_id = ".$mpid;
$result = mysql_query($sql);
$result = mysql_fetch_assoc($result);
echo "<li>".$result['first_name']." ".$result['last_name']."</li>\n";
}
echo "</ul>";

Answer 1

This is your query:
SELECT DISTINCT distance.mp_id
from distance
WHERE distance.distance < 0.2 AND
distance.dream_id IN (SELECT dream_id
from policy
WHERE UPPER(policy.title) LIKE UPPER('%".$keyword."%')
)
ORDER BY distance.distance
LIMIT 5;
In some versions of MySQL, the in with a subquery is inefficient. Let me also assume that mp_id is unique for the table distance. This query might work better:
SELECT d.mp_id
from distance d
WHERE d.distance < 0.2 AND
exists (select 1
from policy p
where UPPER(p.title) LIKE UPPER('%".$keyword."%') and
p.dream_id = d.dream_id
)
ORDER BY d.distance
LIMIT 5;
This query would be further improved by having an index on policy(dream_id) and possibly distance(distance).
Depending on how large the policy table is, one major impediment to performance is the expression UPPER(policy.title) LIKE UPPER('%".$keyword."%'). If you really mean equality, then use equality and not like with wildcards. If you are really storing multiple keywords in the title column, then consider either breaking these out into a separate table or using full text search.