SQL as Control Source for Access Form field

You can set the control source of your field to a function name. That function can easily execute your SQL, and/or pass in a variable. Here's my simple boiler plate for a function to execute a SQL statement into a recordset and return the first value. In my world I'm usually including a very specific where clause, but you could certainly make any of this function more robust for your needs.

=fnName(sVariable, iVariable)

Public Function fnName( _
    sVariable as String, _
    iVariable as Integer _
    ) As String

On Error GoTo Err_fnName

    Dim con As ADODB.Connection
    Dim rst As ADODB.Recordset
    Dim sSQL As String

    sSQL = ""

    Set con = Access.CurrentProject.Connection
    Set rst = New ADODB.Recordset

    rst.Open sSQL, con, adOpenDynamic, adLockOptimistic

        If rst.BOF And rst.EOF Then

            'No records found
            'Do something!

        Else

            'Found a value, return it!
            fnName = rst(0)

        End If

    rst.Close
    Set rst = Nothing

    con.Close
    Set con = Nothing

Exit_fnName:

    Exit Function

Err_fnName:

    Select Case Err.Number
    Case Else
        Call ErrorLog(Err.Number, Err.Description, "fnName", "", Erl)
        GoTo Exit_fnName
    End Select

End Function

Pretty sure that is true SQL, but you could use the function:
=DLookUp("field_name","table_name","any_fieldname = 'value'")

It might be easiest to use a combobox and set the Row Source to your query, alternatively, DAO is native to Access.

Private Sub Form_Current()
''Needs reference to Microsoft DAO 3.x Object Library
Dim db As Database
Dim rs As DAO.Recordset
Dim strSQL As String
Dim strResult  As String


strSQL = "SELECT ci.IssueDesc FROM tblCaseIssues ci " _
       & "INNER JOIN tblCaseNewHS_Issues cni ON ci.ID = cni.IssueID " _
       & "WHERE cni.HS_ID = 81"

Set db = CurrentDb
Set rs = db.OpenRecordset(strSQL)

If rs.RecordCount > 0 Then
    Do While Not rs.EOF
        strResult = strResult & ", " & rs!IssueDesc
        rs.MoveNext
    Loop

    strResult = Mid(strResult, 3)
Else
    strResult = "Not found"
End If

Me.TextBoxName = strResult

End Sub