How to populate a combobox from two different SQL Server database tables - vb.net

Question

I am trying to create a system that will load items from a database. There are two comboboxes; combobox1 which loads items from database table 1 and combox2 which loads items from database table 2.
Both tables are in the same database.
Here is was I tried but when I run the system I get this error:
(Conversion from string "SELECT * FROM dbo.Dishes" to type 'Long' is not valid.)
Here is the code I'm using:
Dim connection As New SqlConnection("Server = DESKTOP-1373H91; Initial Catalog = MealPreOrderSystem; Integrated Security = True")
connection.Open()
Dim query As String = "SELECT * FROM dbo.Dishes" And "SELECT * FROM dbo.Desserts"
Dim cmd As SqlCommand
cmd = New SqlCommand(query, connection)
Dim reader As SqlDataReader
reader = cmd.ExecuteReader
While reader.Read
cbxType.Items.Add(reader.Item("MealName"))
cbxType.Items.Add(reader.Item("DessertName"))
End While
connection.Close()

Answer 1

In VB.NET,AND is an operator.It is used to perform conjunction between either Booleans or Integers/Doubles/any numeric expression.Lets take your query string as an example :
Dim query As String = "SELECT * FROM dbo.Dishes" And "SELECT * FROM dbo.Desserts"
You are using AND here to join 2 sentences/strings which wouldn't result in anything rather it is trying to cast it as a Long.
Try to execute this command in SQL and you won't find any luck :(.
Your statements are correct :
SELECT * FROM dbo.Dishes
SELECT * FROM dbo.Desserts
But the way you are trying to achieve your goals is incorrect :(.
To get the data from the database into your combobox, what you can do is either use two comboboxes with separated SQL Queries/SQL Commands or you can use one combobox where you add data from both the databases but separate them with some special characters such as a comma ,
A sample may look like :
With one combobox
Dim cmd1 as new SqlCommand("SELECT * FROM dbo.Dishes",connection)
Dim dr as SqlDatareader = cmd1.ExecuteReader
While dr.Read
mycombo1.Items.Add(dr(0)) ' Here 0 is the column count,change it as required
End while
Dim cmd2 as new SqlCommand("SELECT * FROM dbo.Desserts",connection)
Dim dr2 as SqlDatareader = cmd2.ExecuteReader
While dr2.Read
mycombo2.Items.Add(dr2(0)) ' Here 0 is the column count,change it as required
End while
With 1 combobox
Here it gets a bit complicated.Firstly you need to populate your combobox from the data received from the first dataReader.Then, when the 2nd datareader is reading the data , you need to update the existing data/Item of the combobox keeping the existing data/item but adding new data/item to each existing data/item(separating them with ,).
Sample :
Dim i as Integer
Dim cmd1 as new SqlCommand("SELECT * FROM dbo.Dishes",connection)
Dim dr as SqlDatareader = cmd1.ExecuteReader
While dr.Read
mycombo1.Items.Add(dr(0))
End while
Dim cmd2 as new SqlCommand("SELECT * FROM dbo.Desserts",connection)
Dim dr2 as SqlDatareader = cmd2.ExecuteReader
While dr2.Read
mycombo1.Items(i) = myconbo1.Items(i) & "," & dr2(0)
i = i + 1
End while
Now, NOTE THAT I AM USING MULTIPLE DATAREADERS WITH THE SAME CONNECTION ,SO YOU MAY NEED TO INCLUDE MultipleActiveResultSets=True IN YOUR CONNECTION STRING or ENCLOSE THE DATAREADERS IN USING STATEMENTS or CALL dataReader.Close AFTER EACH DATAREADER HAS COMPLETED READING FROM THE DATABASE
This will solve your issue :)

Answer 2

Looks like you don't know how to write SQL queries (and your VB syntax itself looks faulty - string AND string?).
Dim connection As New SqlConnection("Server = DESKTOP-1373H91; Initial Catalog = MealPreOrderSystem; Integrated Security = True")
Dim query As String = <cmdString>
SELECT MealName as Name FROM dbo.Dishes
union
SELECT DessertName as Name FROM dbo.Desserts
</cmdString>
Dim cmd As SqlCommand
Dim reader As SqlDataReader
connection.Open()
cmd = New SqlCommand(query, connection)
reader = cmd.ExecuteReader
While reader.Read
cbxType.Items.Add(reader.Item("Name"))
End While
connection.Close()
Note: You are saying 2 comboboxes but your code seemed to be loading all the items to a single combobox. If you really need 2 comboboxes then use 2 SqlCommand and Reader loops (actually it would be better if you simply have used Linq for this).

Answer 3

You should be a bit more specific on what columns you are pulling from the 2 tables. if they are similar, you could write a sql query to UNION ALL the fields with a simple control to identify which record came from which table.
Example of SQL command string:
"SELECT 'M' AS Ctl, MealName AS aName FROM dbo.Dishes " &
"UNION ALL " &
"SELECT 'D' AS Ctl, DessertName AS aName FROM dbo.Desserts"
As mentioned by many here already, it seems like you are referencing only 1 ControlBox to list the fields returned cbxType
below is the reader (adapted to 2 ComboBoxes):
While reader.Read
Select Case reader.Item("Ctl")
Case "M"
cbxMType.Items.Add(reader.Item("aName"))
Case "D"
cbxDType.Items.Add(reader.Item("aName"))
End Select
End While
Hope this helps