Fatal error: Uncaught PDOException: SQLSTATE[21000]: Cardinality violation: 1242 Subquery returns more than 1 row in /var/www/html/experiments/experiment.php:35 Stack trace: #0 /var/www/html/experiments/experiment.php(35): PDOStatement->execute() #1 {main} thrown in /var/www/html/experiments/experiment.php on line 35