How to use group by in SQL Server query?

Question

I have problem with group by in SQL Server

I have this simple SQL statement:

select * 
from Factors 
group by moshtari_ID

and I get

Answer 1

In general, once you start GROUPing, every column listed in your SELECT must be either a column in your GROUP or some aggregate thereof. Let's say you have a table like this:

| ID | Name        | City        |
|  1 | Foo bar     | San Jose    |
|  2 | Bar foo     | San Jose    |
|  3 | Baz Foo     | Santa Clara |

If you wanted to get a list of all the cities in your database, and tried:

SELECT * FROM table GROUP BY City

...that would fail, because you're asking for columns (ID and Name) that aren't in the GROUP BY clause. You could instead:

SELECT City, count(City) as Cnt FROM table GROUP BY City

...and that would get you:

| City        | Cnt |
| San Jose    |  2  |
| Santa Clara |  1  |

...but would NOT get you ID or Name. You can do more complicated things with e.g. subselects or self-joins, but basically what you're trying to do isn't possible as-stated. Break down your problem further (what do you want the data to look like?), and go from there.

Good luck!