SQL语句可查询表中一列的平均值，并从另一张表中联接并查询相应的列

Question

I have two tables, each set up like this

--------------------------    ---------------------------
|           DVD          |    |          Sells          |
--------------------------    ---------------------------
| dvdid | title | length |    | dvdid | storeid | price |
--------------------------    ---------------------------
|   1   | Alpha |   27   |    |   1   |   100   | 11.99 |
--------------------------    ---------------------------

I'm trying to select the average of Sells.price for each DVD.title, and select both. Right now I have the following:

SELECT AVG(Sells.price), DVD.title
FROM Sells inner join DVD on Sells.dvdid = DVD.dvdid;

Unfortunately this does not work, I receive the error "Not a single-group group function. I assume this means I can't SELECT a function like AVG and then a single column to go along with it. Any ideas?

Answer 1

You need to add DVD.title in Group By

SELECT AVG(Sells.price), DVD.title
FROM Sells inner join DVD on Sells.dvdid = DVD.dvdid
Group by DVD.title --Here