Average of grouped rows in Sql Server

问题

I have an Sql Server Table.. it's something like this:

Id ...... Column1 ...... Column2  
````````````````````````````````  
1 ........ 1 ............. 34  
2 ........ 1 ............. 44  
3 ........ 2 ............. 45  
4 ........ 2 ............. 36  
5 ........ 2 ............. 23  
6 ........ 3 ............. 68  
7 ........ 3 ............. 26

So, I need to select the average of Column2,but group with column1 before doing that.
I mean, if I say Avg(Column2) it just returns a single row with the average of all rows.

What I need is, first i need to group them by column so:
Average of column2 where column1 = 1
Average of column2 where column1 = 2
Average of column2 where column1 = 3

So I want 3 rows returned with the averages of respective values of column1. I am lost at doing this, any hints / help please?

ps: I tried several related questions, and none of them helped / I couldn't understand.

回答1:

Is this what you want?

select column1, avg(column2) from table group by column1

回答2:

simple

select AVG(Column2) from table group by Column1

doesn't work?

回答3:

SELECT column1, AVG(column2) 
  FROM "Insert table name"
GROUP BY column1

回答4:

SELECT Column1, AVG(Column2) FROM test GROUP BY Column1;

回答5:

This following Query will help for Calculate the average value of a ROW:

 select Avg(A.Tamil + A.English + A.Maths + A.Science + A.Social_Science)/5 As 
 Average
 from MarkTable A, MarkTable B, MarkTable C
 where A.RollNo='14UCA002'

This might helpful...

回答6:

Execute the following SQL from average :

select column1,avg(column2) from tablename group by column1;

来源：https://stackoverflow.com/questions/3100921/average-of-grouped-rows-in-sql-server

标签

sql-server

average