How to Update MySQL Train Capacity Using Multi-Table UPDATE Syntax After Reservation Cancellation?

MySQL Join Update Syntax for Capacity Modification

When updating multiple tables in MySQL, the multi-table UPDATE syntax can be employed. Let's explore how to leverage this syntax to resolve a use case where we need to increment the capacity of a train based on a reservation cancellation.

Problem Statement:

Consider two tables, Train and Reservations. We want to increase the capacity of a specific train when a reservation is canceled.

Train
+----------+-------------+------+-----+---------+-------+
| Field    | Type        | Null | Key | Default | Extra |
+----------+-------------+------+-----+---------+-------+
| TrainID  | varchar(11) | NO   | PRI | NULL    |       |
| Capacity | int(11)     | NO   |     | 50      |       |
+----------+-------------+------+-----+---------+-------+

Reservations
+---------------+-------------+------+-----+---------+----------------+
| Field         | Type        | Null | Key | Default | Extra          |
+---------------+-------------+------+-----+---------+----------------+
| ReservationID | int(11)     | NO   | PRI | NULL    | auto_increment |
| FirstName     | varchar(30) | NO   |     | NULL    |                |
| LastName      | varchar(30) | NO   |     | NULL    |                |
| DDate         | date        | NO   |     | NULL    |                |
| NoSeats       | int(2)      | NO   |     | NULL    |                |
| Route         | varchar(11) | NO   |     | NULL    |                |
| Train         | varchar(11) | NO   |     | NULL    |                |
+---------------+-------------+------+-----+---------+----------------+

Solution:

Using the multi-table UPDATE syntax, we can increment the Capacity column in the Train table based on the NoSeats value in the Reservations table, given a specific ReservationID.

UPDATE Reservations r JOIN Train t ON (r.Train = t.TrainID)
SET t.Capacity = t.Capacity + r.NoSeats
WHERE r.ReservationID = ?;

Alternatively, to increment by an arbitrary number of seats, simply change r.NoSeats to the desired value in the above query.

Transaction Considerations:

Yes, you can increment and delete within a Java transaction. To ensure data integrity, perform the update operation first, followed by the deletion.

By using the multi-table UPDATE syntax, we can efficiently update the Train table and modify its Capacity value based on reservation cancellation, thus maintaining synchronized data across multiple tables.

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