Attribute A based on Attribute B (Microsoft SQL Server 2014)

Question

For example I have two tables named Manager_Order and Book_Inventory.

Manager_Order(
  ID (PK),
  Book_Name,
  Quantity (Attribute A)
)

Book_Inventory(
  ID (PK),
  Book_Name (FK on Manager_Order),
  Quantity (Attribute B)
)

Everytime manager makes an order, I want the Quantity in Book_Inventory updates automatically.

Answer 1

Look into using an after update trigger.

Here is an example (not tested):

CREATE TRIGGER [dbo].Update_Book_Inventory
ON [dbo].Manager_Order  
FOR  UPDATE
AS
BEGIN
    SET NOCOUNT ON;
      UPDATE [dbo].Book_Inventory
        SET Quantity = i.Quantity
            FROM [dbo].Book_Inventory
            INNER JOIN INSERTED i ON [dbo].Book_Inventory.Book_Name = i.Book_Name
END

Reference: https://www.mssqltips.com/sqlservertip/4024/sql-server-trigger-after-update-for-a-specific-value/