framework/db/conditions/ExistsConditionBuilder.php
public function build(ExpressionInterface $expression, array &$params = [])
    {
        $operator = $expression->getOperator();
        $query = $expression->getQuery();

        $sql = $this->queryBuilder->buildExpression($query, $params);

        return "$operator $sql";
    }
public function build(ExpressionInterface $expression, array &$params = [])
    {
        $operator = $expression->getOperator();
        $query = $expression->getQuery();

        $sql = $this->queryBuilder->buildExpression($query, $params);

        return "$operator $sql";
    }
Method builds the raw SQL from the $expression that will not be additionally
escaped or quoted.

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