Why Does My Parameterized Query Throw a 'Parameter Not Supplied' Error?

"The Parameterized Query Expects the Parameter Which Was Not Supplied"

When attempting to execute a parameterized query with a textbox input as a parameter, users often encounter this error. To rectify this issue, it's crucial to ensure that the parameter value is properly set before executing the query.

Root Cause:

Parameterized queries use placeholders (e.g., "@Parameter1") to represent values that will be provided dynamically during execution. If a parameter is not supplied or its value is null, the query will fail.

Solution:

1. Add Parameter to Query:

   cmd.Parameters.Add("@Department", SqlDbType.VarChar)

   This creates a parameter named "@Department" that will accept a string value.

2. Handle Null Values:

   If the textbox input could potentially be empty (null), check for it and assign DBNull.Value accordingly:

   If (TextBox2.Text = Nothing) Then
       cmd.Parameters("@Department").Value = DBNull.Value
   Else
       cmd.Parameters("@Department").Value = TextBox2.Text
   End If

   This ensures that you don't pass a null value directly, which is not accepted by parameterized queries.

By following these steps, the parameters will be correctly set and the query will execute successfully. Remember to consider null values when working with parameterized queries to avoid common errors.

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