function Select::prepareCountQuery

Prepares a count query from the current query object.

Return value

\Drupal\Core\Database\Query\Select A new query object ready to have COUNT(*) performed on it.

File

core/lib/Drupal/Core/Database/Query/Select.php, line 743

Class

Select

Query builder for SELECT statements.

Namespace

Code

protected function prepareCountQuery() {
    // Create our new query object that we will mutate into a count query.
    $count = clone $this;
    $group_by = $count->getGroupBy();
    $having = $count->havingConditions();
    if (!$count->distinct && !isset($having[0])) {
        // When not executing a distinct query, we can zero-out existing fields
        // and expressions that are not used by a GROUP BY or HAVING. Fields
        // listed in a GROUP BY or HAVING clause need to be present in the
        // query.
        $fields =& $count->getFields();
        foreach (array_keys($fields) as $field) {
            if (empty($group_by[$field])) {
                unset($fields[$field]);
            }
        }
        $expressions =& $count->getExpressions();
        foreach (array_keys($expressions) as $field) {
            if (empty($group_by[$field])) {
                unset($expressions[$field]);
            }
        }
        // Also remove 'all_fields' statements, which are expanded into tablename.*
        // when the query is executed.
        foreach ($count->tables as &$table) {
            unset($table['all_fields']);
        }
    }
    // If we've just removed all fields from the query, make sure there is at
    // least one so that the query still runs.
    $count->addExpression('1');
    // Ordering a count query is a waste of cycles, and breaks on some
    // databases anyway.
    $orders =& $count->getOrderBy();
    $orders = [];
    if ($count->distinct && !empty($group_by)) {
        // If the query is distinct and contains a GROUP BY, we need to remove the
        // distinct because SQL99 does not support counting on distinct multiple fields.
        $count->distinct = FALSE;
    }
    // If there are any dependent queries to UNION, prepare each of those for
    // the count query also.
    foreach ($count->union as &$union) {
        $union['query'] = $union['query']->prepareCountQuery();
    }
    return $count;
}