SQL 如何根据另一个值自动增加一个值

Question

I am creating a program where I am using a SQL Database, but I have a problem on how to solve the following problem.

I have a table named Warehouse where I have WarehouseID and a WarehouseName.

Then, I created another table named Aisle where I have WarehouseID (which should be the same field as before) and AisleID and AisleName.

So WarehouseID and AisleID can be 1, 2, 3... But what I want is that when I select WarehouseID = 1 to create a new AisleID, the database should be able to notice which is the last number of AisleID for WarehouseID = 1 and add an autoincrement.

So, can be multiple AisleID with the same value but only a WarehouseID with one unique value.

How can I do that in SQL?

Thanks and Kind Regards

Answer 1

This query:

SELECT COALESCE(MAX(AisleID), 0) + 1
FROM Aisle
WHERE WarehouseID = 1

returns the new AisleID that you want to insert in the table Aisle .
But what value do you want for AisleName ?
If AisleName is the same for all rows in Aisle with the same WarehouseID you could use MAX(AisleName) , or if it's not you must supply that value.

So you can do this:

INSERT INTO Aisle(AisleID, AisleName, WarehouseID)
SELECT COALESCE(MAX(AisleID), 0) + 1, MAX(AisleName), ?
FROM Aisle
WHERE WarehouseID = ?

Replace ? with the value of WarehouseID that you want the row to have.
Also replace MAX(AisleName) with the new value of AisleName if you want it to be different than the previous rows, or if it is the first row with that WarehouseID .