Why Am I Getting Null Results When Using PHP PDO Prepared Statements with MySQL LIKE Queries?

PHP PDO Prepared Statement MySQL LIKE Query: Resolve Null Results

In MySQL, a common operation involves querying data using a LIKE clause to perform wildcard searches. When using PHP's PDO class with MySQL, it's essential to understand how to correctly craft these queries to avoid null results.

Let's examine a scenario where a LIKE query is not returning results through the PDO class. The original query in the MySQL client is:

<code class="sql">SELECT    hs.hs_pk, 
          hs.hs_text, 
          hs.hs_did, 
          hd.hd_did, 
          hd.hd_text, 
          hv.hv_text, 
          hc.hc_text 
FROM      hs 
LEFT JOIN hd 
 ON       hs.hs_did = hd.hd_did 
LEFT JOIN hd 
 ON       hd.hd_vid = hv.hv_id 
LEFT JOIN hc 
 ON       hd.hd_pclass = hc.hc_id
WHERE     hs.hs_text LIKE "%searchTerm%"
LIMIT 25;</code>

This query leverages the LIKE operator to find all rows where the hs.hs_text column contains the searchTerm within its value. However, when this query is translated into PHP's PDO class, it fails to return any results.

<code class="php">$sql = 
'SELECT   hs.hs_pk, 
          hs.hs_text, 
          hs.hs_did, 
          hd.hd_did, 
          hd.hd_text, 
          hv.hv_text, 
          hc.hc_text 
FROM      hs 
LEFT JOIN hd 
 ON       hs.hs_did = hd.hd_did 
LEFT JOIN hd 
 ON       hd.hd_vid = hv.hv_id 
LEFT JOIN hc 
 ON       hd.hd_pclass = hc.hc_id
WHERE     hs.hs_text LIKE :searchTerm
LIMIT 25';

$ret = $prep->execute(array(':searchTerm' => '"%'.$searchTerm.'%"'));</code>

The issue in the PHP code is the presence of double quotes around the searchTerm in the WHERE clause. Prepared statements in PHP do not require quotes when binding values. Quotes are only needed when string values are directly embedded into the query itself.

To resolve the issue, simply remove the double quotes from the searchTerm parameter:

<code class="php">$ret = $prep->execute(array(':searchTerm' => '%'.$searchTerm.'%'));</code>

This modification allows the PDO class to correctly bind the searchTerm value to the query, which will produce the expected results.

Prepared statements provide increased security and efficiency by separating data from the query. They prevent SQL injection vulnerabilities and optimize query execution by allowing the database to handle the binding process. Understanding how to correctly use LIKE queries with PHP's PDO class is essential for effective data retrieval from MySQL databases.

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