The information in this article applies to:
- ActiveX Data Objects (ADO), versions 1.0, 1.5
SYMPTOMS
Under certain conditions with ActiveX Data Objects (ADO), SELECT DISTINCT
in your SQL statement will not provide distinct records. However, you have
to meet all of the following conditions to cause the problem to occur:
- You opened a standalone ADO recordset without opening it off a
Command or Connection object.
- The data source you are opening is SQL Server.
- The recordset CursorLocation is set to adUseClient.
This happens when either the Recordset.Open method is used or when the
recordset is obtained from a command object by setting the recordset equal
to the return value of Command.Execute.
CAUSE
The reason this does not work with adUseClient is that ADO uses SQL
Server's FOR BROWSE option on the SQL statement to get extended metadata in
order to process updates. The use of this option causes SQL version 6.5 to
ignore the DISTINCT keyword.
RESOLUTION
Here are the two possible workarounds to get SELECT DISTINCT to work as
expected:
- Set the CursorLocation to adUseServer instead of adUseClient.
- When using the Open method with adUseClient you can workaround this
problem by using a command object and setting its ActiveConnection to
the connection used in the Open statement.
The Steps to Reproduce Behavior below demonstrates the workarounds for both
the Open and the Command methods.
STATUS
Microsoft is researching this problem and will post new information here in
the Microsoft Knowledge Base as it becomes available.
MORE INFORMATION
Steps to Reproduce Behavior
- Create a standard .exe project, and under Project, References select
Microsoft ActiveX Data Objects 1.5 Library.
- Paste the following code in the Declaration section of the form:
Option Explicit
Dim conn As New Connection
'Dim com As New Command 'Uncomment to make DISTINCT work.
Dim rs As New Recordset
Private Sub Command1_Click()
conn.open "mymachine", "sa", ""
conn.cursorlocation = adUseClient 'Change to aduseServer.
'com.ActiveConnection = conn 'Uncomment to make DISTINCT work.
rs.open "select distinct state from authors", conn, _
adOpenKeyset, adLockOptimistic
MsgBox rs.RecordCount
End Sub
Private Sub Command2_Click()
Dim counter As Integer
counter = 0
conn.Open "dsn=mymachine;id=sa;pwd=;"
com.ActiveConnection = conn
conn.CursorLocation = adUseClient 'Comment this
'conn.CursorLocation = adUseServer 'and uncomment this.
com.CommandText = "select distinct state from authors"
com.CommandType = adCmdText
rs.CursorType = adOpenKeyset
'cursortype will be adopenforwardonly with adUseServer.
Set rs = com.Execute
While Not rs.EOF
Debug.Print rs!State
counter = counter + 1
rs.MoveNext
Wend
Debug.Print "--------------------"
MsgBox counter 'recordcount return -1 with adUseServer
End Sub
- Run the code and click Command1. Note the number of records returned.
Change adUseClient to adUseServer in the CursorLocation. Run the code
again and fewer records are returned if there are duplicate states.
- Change aduseServer back to adUseClient. Uncomment the Dim of the command
object and the code in Command1. Run the code again. You receive the
correct number of records using this technique also.
- Run the code again and click Command2. Note the counter. Comment the
CursorLocation for adUseClient and uncomment the adUseServer
CursorLocation. Run the code and note the counter again.
Keywords : kbcode adoall adogenis
Version : WINDOWS:1.0,1.5
Platform : WINDOWS
Issue type : kbprb
Solution Type : kbnofix