Try this for debugging SQL queries
$this->logger->debug($select->getSqlString());
throws a Notice: Attempting to quote a value without specific driver level support can introduce security vulnerabilities in a production environment.
To get also (not only remove the notice) a correct SQL query:
$this->logger->debug($select->getSqlString($this->adapter->getPlatform()));
For Platform MySQL it makes not correct query. An integer from SQL query LIMIT part
$select->limit(1);
give me
LIMIT '1'
what throws an error in MySQL.
Correct is
LIMIT 1