Visual Studio 2012 中的 SQL 查询错误

Question

我正在尝试写一些可以在工作中使用并且正在自学的东西。我遇到了一个我找不到解决方案的问题，尽管我很可能只是不熟悉正确的术语。

我已将 Visual Studio 项目附加到 SQL 数据库，并尝试执行搜索，我可以在三个文本框中的任何一个中输入信息，它会相应地过滤返回的结果。这是用户搜索查询：

SELECT        First_Name AS [First Name], Middle_Name AS [Middle Name], Last_Name AS [Last Name], Users_ID AS [Unique ID]
FROM            Users
WHERE        (First_Name LIKE '%' + @firstName + '%') AND (Last_Name LIKE '%' + @lastName + '%') AND (Users_ID LIKE '%' + @uniqueID + '%')
ORDER BY [Last Name]

这是我用来调用搜索的 SUB。我唯一遇到的问题是用户搜索。

Private Sub searchButton_Click(sender As Object, e As EventArgs) Handles searchButton.Click
    'Clear all variables when the search button is clicked.  This allows Search to start with a clean'
    'slate and gather new or changed variables again.'
    addRemoveValue = Nothing
    jobTitle = Nothing
    jtLocation = Nothing
    jtDepartment = Nothing
    loc = Nothing
    lComments = Nothing
    department = Nothing
    fname = Nothing
    lname = Nothing
    uID = Nothing

    'Gather variables.'
    addRemoveValue = TryCast(addRemoveComboBox.SelectedItem, String)
    jobTitle = TryCast(jobTitleTextBox.Text, String)
    jtLocation = TryCast(jtLocationComboBox.Text, String)
    jtDepartment = TryCast(jtDepartmentComboBox.Text, String)
    loc = TryCast(locationTextBox.Text, String)
    lComments = TryCast(lCommentsTextBox.Text, String)
    department = TryCast(departmentTextBox.Text, String)
    fname = TryCast(firstNameTextBox.Text, String)
    lname = TryCast(lastNameTextBox.Text, String)
    uID = TryCast(uniqueIDTextBox.Text, String)

    'I added this in order to troubleshoot the search feature for the Users search.'
    'If uID = Nothing Then'
    '    uID = "%"'
    'End If'

    'Change the visible buttons in the event of a Search.'
    disableButton.Visible = True
    addButton.Visible = False

    'Populate the Data Grid based on the item the user selects.'
    If addRemoveValue = "Job Title" Then
        With Me.DataGridView1
            .AutoGenerateColumns = True
            .DataSource = RoleTableAdapter.GetDataByTitle(jobTitle, jtLocation, jtDepartment)
            .AutoSizeRowsMode = DataGridViewAutoSizeRowsMode.DisplayedCellsExceptHeaders
            .AutoSizeColumnsMode = DataGridViewAutoSizeColumnMode.DisplayedCells
            .BorderStyle = BorderStyle.Fixed3D
            .EditMode = DataGridViewEditMode.EditOnEnter
        End With
    End If

    If addRemoveValue = "Location" Then
        With Me.DataGridView1
            .AutoGenerateColumns = True
            .DataSource = LocationTableAdapter.GetDataByLoc(loc)
            .AutoSizeRowsMode = DataGridViewAutoSizeRowsMode.DisplayedCellsExceptHeaders
            .AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.DisplayedCells
            .BorderStyle = BorderStyle.Fixed3D
            .EditMode = DataGridViewEditMode.EditOnEnter
        End With
    End If

    If addRemoveValue = "Department" Then
        With Me.DataGridView1
            .AutoGenerateColumns = True
            .DataSource = DepartmentTableAdapter.GetDataByDept(department)
            .AutoSizeRowsMode = DataGridViewAutoSizeRowsMode.DisplayedCellsExceptHeaders
            .AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.DisplayedCells
            .BorderStyle = BorderStyle.Fixed3D
            .EditMode = DataGridViewEditMode.EditOnEnter
        End With
    End If

    If addRemoveValue = "User" Then
        With Me.DataGridView1
            .AutoGenerateColumns = True
            .DataSource = UsersTableAdapter.GetDataByName(uID, fname, lname)
            .AutoSizeRowsMode = DataGridViewAutoSizeRowsMode.DisplayedCellsExceptHeaders
            .AutoSizeColumnsMode = DataGridViewAutoSizeColumnsMode.DisplayedCells
            .BorderStyle = BorderStyle.Fixed3D
            .EditMode = DataGridViewEditMode.EditOnEnter
            .Columns("Unique ID").DisplayIndex = 0
            .Columns("Last Name").DisplayIndex = 1
            .Columns("First Name").DisplayIndex = 2
            .Columns("Middle Name").DisplayIndex = 3
        End With
    End If
End Sub

每当我对此进行测试时，都会收到以下错误：

未能启用约束。一行或多行包含值 违反非空、唯一或外键约束。

我查看了所有列的属性，所有列都可以包含 NULL 值。我已经查看并确保我的任何表上都没有外键约束。我不知道接下来要寻找什么来解决这个问题，因为我在这段代码中的其他三个搜索工作得很好，而且他们有非常相似的查询。

您能提供的任何帮助都会很棒！谢谢！！

Answer 1

是否存在名字、姓氏和/或用户 ID 可能为空的情况？

如果您更改数据库中的列长度但不更新数据集，有时也会弹出此错误。