Select all data from 1 column - sql

Question

I have code that is supposed to take all "course names" from a module based on what school is chosen.
For example the school of biology has the modules "biochemistry" and "marine biology". I need to select both of these in order to use in a calculation.
Currently when the code is run it will only take the first module ie "biochemistry" but I need it to select all of the modules.
Can anyone help?
Dim courseSelectCom As New SqlCommand("SELECT course_name FROM course where school= '%"schoolSelect & "' ", _
connection)

Answer 1

The first thing to do on your query is to use a parametrized query.
This will avoid Sql Injection and parsing problems.
Then you shoud explain why you use the wildcard % in front of SchoolSelect.
Do you have many kind of schools that ends with the same suffix and do you want to retrieve all of them?
Last, you should use a DataReader to loop over the returned data or a DataAdapter to fill a DataTable.
So summarizing
Dim sb = new StringBuilder()
Using connection = New SqlConnection("your_con_string_here")
connection.Open()
Dim courseSelectCom = New SqlCommand("SELECT course_name FROM course where school=#schoolName", connection)
courseSelectCom.Parameters.AddWithValue("#schoolName", SchoolSelect.Text)
Dim reader = courseSelectCom.ExecuteReader()
while reader.Read()
sb.AppendLine(reader("course_name")) ' or add to some kind of list to reuse'
End While
End Using
Console.WriteLine(sb.ToString())
if you want to store the data in a DataTable then replace the DataReader loop with
Dim dt = New DataTable()
Dim da = New SqlDataAdapter(courseSelectCom)
da.Fill(dt)
And you have a DataTable object to use for binding to a DataGridView, Listbox or whatever....

Answer 2

What are you using for Executing the command?
If you use ExecuteScalar you will get only first result.
Use ExecuteReader and read through or Use DataAdapter and fill a DataSet with it.

Answer 3

Dim courseSelectCom As New SqlCommand("SELECT course_name FROM course where school=#School", _connection)
courseSelectCom.Parameter.Add("#School", SqlDbType.VarChar).Value = SchoolSelect.Text
SchoolSelect is the textbox from which you select school

Answer 4

If you want all the courses in a comma delimited list, then use group_concat (assuming you are using MySQL):
SELECT group_concat(course_name)
FROM course
where school= '%"schoolSelect & "'
This returns one row, with all the courses in a single column, like 'biochemistry,marine biology'.
To do this in SQL Server, you can do:
select stuff((select ','+course_name from course where school= '%"schoolSelect & "' for xml path ('')),
1, 1, '') as coursenames
SQL Server does not have a native aggregate string concatenation operator, so this uses XML features of the database.
I think it would be written as:
Dim courseSelectCom = New SqlCommand("select stuff((select ','+course_name from course where school= '%"schoolSelect & "' for xml path ('')), 1, 1, '') as coursenames", connection)
You need something like this:
Dim reader = courseSelectCom.ExecuteReader()
reader.Read()
reader("course_names")