How to use if condition using two tables in MySQL - mysql

Question

Can anyone help me on this? What I wanted to happen is that if the value exist in Table 1 (employee), it will then check Table 2 (mobilelist) if it also exist there. Here's the code:
Private Sub TextBox_IDNumber_LostFocus(sender As Object, e As EventArgs) Handles TextBox_IDNumber.LostFocus
Mysqlconn = New MySqlConnection
Mysqlconn.ConnectionString = "server=localhost;userid=root;password=12345;database=my_db"
Dim READER As MySqlDataReader
Dim READER2 As MySqlDataReader
Dim _isFound As Boolean = False
Dim _isExist As Boolean = False
Try
Mysqlconn.Open()
Dim empmr As String
Dim empml As String
Dim fn1 As String
Dim fn2 As String
Dim ln1 As String
Dim ln2 As String
empmr = "Select * from my_db.employee where IDNumber ='" & TextBox_IDNumber.Text & "'"
empml = "Select * from my_db.mobilelist where IDNumber = '" & TextBox_IDNumber.Text & "' AND DateAssigned is not Null AND DateReturned is Null"
Command = New MySqlCommand(empmr, Mysqlconn)
READER = Command.ExecuteReader
While READER.Read()
_isFound = True
fn1 = READER.GetString("FirstName")
ln1 = READER.GetString("LastName")
End While
If _isFound Then
TextBox_FirstName.Text = fn1
TextBox_LastName.Text = ln1
ElseIf Not _isExist Then
MessageBox.Show("Record Not Found in Master Data")
TextBox_IDNumber.Clear()
TextBox_FirstName.Clear()
TextBox_LastName.Clear()
TextBox_IDNumber.Focus()
End If
Catch ex As MySqlException
MessageBox.Show("Error!")
Finally
Mysqlconn.Dispose()
End Try
End Sub

Answer 1

Assuming you have the appropriate Primary Key and Foreign Key relationship between the tables Employee and MobileList you use this query to find records on the MobileList table for an employee:
Dim myQuery as string
myQuery = "SELECT FirstName, LastName, MobileNumber
FROM Employee
JOIN MobileList
ON Employee.IDNumber=MobileList.IDNumber
WHERE Employee.IDNumber=#ID"
Note: You should rename the IDNumber column on the MobileList to avoid confusion.
You should also improve your access to the database with the Using statement and take advantage of Parameters to prevent SQL injection:
Using myConn As New SqlConnection("Your connection string")
myConn.Open()
Using myCmd As New SqlCommand(myQuery, myConn)
myCmd.Parameters.AddWithValue("#ID", "Your ID value")
Using myReader As SqlDataReader = myCmd.ExecuteReader()
If myReader.HasRows Then
'There are mobile numbers issued to that ID'
Do While myReader.Read()
'Iterate through all existing records'
Loop
Else
'There are no mobile numbers issued to that ID'
End If
End Using
End Using
End Using
Keep in mind that this gives you the mobile numbers for a particular employee, it doesn't tell you if a particular employee exists.