Question

I use SQL Server 2008, C#, I have a table which contains about 20000 rows, I have several similar rows in this table, there are about 900 distinct rows, it is my table structure:

tblCourse

courselevel, coursecode, coursename, branchcode...

For example I have 20 rows with the same coursecode/coursename but with different branchcode or courselevel, I’m going to have a table which contains item with only unique coursecode.

here is a little sample of my table:

... courselevel=1,coursecode=1200,coursename=A,branchcode=200...
... courselevel=2,coursecode=1200,coursename=A,branchcode=200...
... courselevel=1,coursecode=1200,coursename=A,branchcode=220...
... courselevel=1,coursecode=1200,coursename=A,branchcode=230...
... courselevel=1,coursecode=1200,coursename=A,branchcode=240...
... courselevel=1,coursecode=1200,coursename=A,branchcode=250...
... courselevel=2,coursecode=1200,coursename=A,branchcode=251...
... courselevel=1,coursecode=1200,coursename=A,branchcode=225...

I want to have only the first row:

... courselevel=1,coursecode=1200,coursename=A,branchcode=200...

because all rows have similar coursecode,

What should I do?

How should I write my select query string?

I have tested different methods (group by, distinct, max(ID)…) with no luck, please help me!

thanks

Answer 1

You can GROUP BY the similar columns and use any Aggregate Function on the other columns to have them just return one record. What that one value would be entirely depends on the aggregate function you use.

Aggregate Functions

Aggregate functions perform a calculation on a set of values and
return a single value. Except for COUNT, aggregate functions ignore
null values. Aggregate functions are frequently used with the GROUP BY
clause of the SELECT statement

In this example, I have used the min/max and avg aggregate functions.

SELECT  courselevel
        , coursecode
        , coursename
        , MIN(branchcode)
        , MAX(othercolumn)
        , AVG(numberColumn)
        , ...
FROM    yourTable
GROUP BY
        courselevel
        , coursecode
        , coursename