framework/db/conditions/ConjunctionConditionBuilder.php
public function build(ExpressionInterface $condition, array &$params = [])
    {
        $parts = $this->buildExpressionsFrom($condition, $params);

        if (empty($parts)) {
            return '';
        }

        if (count($parts) === 1) {
            return reset($parts);
        }

        return '(' . implode(") {$condition->getOperator()} (", $parts) . ')';
    }
public function build(ExpressionInterface $condition, array &$params = [])
    {
        $parts = $this->buildExpressionsFrom($condition, $params);

        if (empty($parts)) {
            return '';
        }

        if (count($parts) === 1) {
            return reset($parts);
        }

        return '(' . implode(") {$condition->getOperator()} (", $parts) . ')';
    }
Method builds the raw SQL from the $expression that will not be additionally
escaped or quoted.

@param ExpressionInterface|ConjunctionCondition $condition the expression to be built.
@param array $params the binding parameters.
@return string the raw SQL that will not be additionally escaped or quoted.