如何将 DATETIME 类型用于变量？

Question

What I want to do is make a variable date_arrived that stores a date and time value when a Client makes a Reservation for a hotel room. Then, I want to Insert into the table a date and time value. The only way I can think of doing this is like so:

CREATE TABLE Reservation
(
    id_reservation SMALLINT IDENTITY(1 ,1) PRIMARY KEY,
    date_arrived DATETIME NOT NULL
)

INSERT INTO Reservation 
VALUES ( ??? );

But I've seen people use the DATETIME type with @datetime syntax but I don't understand this and don't know if it will work with my example. I know using varchar(n) is not convenient. So what is the best way to register a date and time values into a variable?

Answer 1

I think you're confusing what you're asking for, it sounds like what you need is along the lines of:

(You haven't tagged your database but it looks like SQL Server syntax)

CREATE TABLE Reservation
(
    Reservation_Id INT NOT NULL IDENTITY(1 ,1) PRIMARY KEY,
    Booking_Date DATETIME NOT NULL default (GETDATE()),
    Arrival_Date DATETIME NOT NULL,
    Duration TINYINT NOT NULL default(1),
    Checkout_Date as DATEADD (day, Duration, Arrival_date)
)

• Reservation_Id will link you to your other data for the reservation eg guests.
• Booking_Date is "right now" when you insert the data, ie are making the booking, the date on which they booked - this is automatically populated
• Arrival_Date is the date/time they are due to arrive/room reserved for etc, you populate this
• Duration - how many days/nights etc
• Checkout_Date - you don't fill this in, it's caclulated from the Arrival_Date + Duration

You would insert data, assuming your values are passed as two variables,

insert into Reservation (Arrival_Date, Duration)
values (@ArrivalDate, @Duration)
select SCOPE_IDENTITY() --< returns the Reservation_Id for use elsewhere.

Answer 2

You can insert value as:

Insert into reservation values(now());

Answer 3

In MySQL you can use now() for inserting values in your table.

This can be taken care of by the database as well here is a syntax for this.

CREATE TABLE Reservation(id_reservation SMALLINT IDENTITY(1,1) PRIMARY KEY,
    date_arrived DATETIME Default now() NOT NULL)

Here is an example to fill values explicitly.

INSERT INTO reservation (id_reservation,date_arrived) VALUES (678,'2020-11-10 11:26:27');