SQL Server query from 2 tables with grouping and average calc

Question

I've got 2 tables in SQL Server database:

• table_1: [id], [opt_1], [opt_2], [opt_3], [opt_4]
• table_2: [id], [result]

What I need is query that returns table with grouped records by [opt_1] and [opt_2] like this:

[opt_1],
[opt_2],
{count of such records from table_1},
{count of such records from table_2, by [id]},
{average [result] from table_2, by [id]}

What is the best way to get it?

Answer 1

You could use join and group by ;

select t1.opt_1,t2.opt_2,count(t1.id),AVG(t2.result) from table1 t1 
inner join table2 t2 ON t1.id = t2.id
group by t1.opt_1,t2.opt_2