Description:
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The PDO quote method for Informix escapes single quotes inside string with a backslash which is invalid. A single quote should be escaped with another single quote ('TEST\'N%' is incorrect and breaks the query while 'TEST''N%' works).

Test script:
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$pdo = new PDO();
$string = "TEST'N";
$search_string = $pdo->quote($string . "%");
$sql = "SELECT * FROM companies WHERE UPPER(name) LIKE $search_string LIMIT 1";
$query = $pdo->prepare($sql);
$query->execute();
$result = $query->fetchAll(PDO::FETCH_ASSOC);
print_r($result);

Expected result:
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No errors

Actual result:
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Fatal error: Uncaught PDOException: SQLSTATE[HY000]: General error: -11060 [Informix][Informix ODBC Driver]General error.