Drupal 8 Query Alter Group By (views)

index.php

<?php

function module_query_views_events_alter(Drupal\Core\Database\Query\AlterableInterface $query){

        // If this the right query
        if(
            $query->getMetaData('view') != ''
            && $query->getMetaData('view')->getDisplay()->display['id'] == 'block_3'
        ){

            // loop over fields in SELECT
            $fields =& $query->getFields();
            foreach($fields as $fieldIndex => $field){
                // Add an expression to the query, necessary as drupal sets
                $query->addExpression('MIN('.$field['table'].'.'.$field['field'].')', $field['alias']);
                // Remove field from select
                unset($fields[$fieldIndex]);
            }

            // Set group by
            $query->groupBy('node__field_date.entity_id');
          
        }
    }