John Davidson

Message:

I am working on a php project where I need a dynamic column to be part of the sql query result, I have a trips table where each one might have many travels, the trip status is always calculated dynamically according to the several conditions below:

public static function getTripStatus($item)

    {

        $status = 'Unknown';

        if ($item->is_canceled == true) {

            $status = 'canceled';

        } elseif ($item->travels->count() == $item->travels->where('status', 'open')->count()) {

            $status = 'open';

        } else if ($item->travels->count() > 0 && $item->travels->count() == $item->travels->where('status', 'finished')->count()) {

            $status = 'finished';

        } elseif ($item->travels->where('status', 'started')->count() > 0) {

            $status = 'started';

        }



        return $status;

    }

I need to convert the function below to an SQL function so that the status column is dynamically appended to the query result.

---

My Answer:
You can achieve this by using a CASE statement in your SQL query. Here is an example of how you can convert the PHP function to an SQL function:

sql
SELECT
trips.*,
CASE
WHEN trips.is_canceled = 1 THEN 'canceled'
WHEN COUNT(travels.id) = SUM(CASE WHEN travels.status = 'open' THEN 1 ELSE 0 END) THEN 'open'
WHEN COUNT(travels.id) > 0 AND COUNT(travels.id) = SUM(CASE WHEN travels.status = 'finished' THEN 1 ELSE 0 END) THEN 'finished'
WHEN SUM(CASE WHEN travels.status = 'started' THEN 1 ELSE 0 END) > 0 THEN 'started'
ELSE 'Unknown'
END AS status
FROM trips
LEFT JOIN travels ON trips.id = travels.trip_id
GROUP BY trips.id


In this SQL query, we are using a CASE statement to check the conditions for determining the trip status. We are joining the trips table with the travels table and then grouping the results by the trip id. The status column is dynamically calculated based on the conditions specified in the CASE statement.