SQL：为其显示不同的项目和其他实例的数量

Question

I have a table called Inventory that has 2 columns called Item_ID and Color. There are many cases where the same Item_ID has multiple listings with different colors:

Item_ID(1, 1) Color(Blue, Green)

I have to display a listing of all the DISTINCT Item_ID's and also the number of colors each distinct Item_ID comes in.

I know to use SELECT DISTINCT Item_ID AS Item_ID FROM Inventory; in order to get a listing of all the distinct Item_IDs, but I have no clue how to get a listing of the amount of colors each distinct Item_ID comes in.

For the Table, I would like to display: Item_ID: 1, Colors: 2

Answer 1

You can do group by on item_ID to count colors per item

    SELECT DISTINCT Item_ID AS    
    Item_ID , COUNT(Color) as   
    ColorCount FROM Inventory
    GROUP BY Item_ID