The code in VB.NET:
Me.OracleSelectCommand1.CommandText = "SELECT authors FROM a WHERE (state IN :PARAM1)"

In a web browser, user will need to type state.
Here I tried to enter
('CA', 'MN') or
'CA', 'MN' or
CA, MN
I got no result.
But if I entered only CA (not 'CA'), it worked.

Can somebody help?
Thanks.

Did you try entering the following?
(CA, MN)

You might also try changing the select statement to:
"SELECT authors FROM a WHERE state IN (:PARAM1)"

That may not help but it shouldn't hurt.

yeah..i've tried those two..
still doesn't work.
thanks anyway

Sounds to me like it may be time to add a bit more code to the processing. You could let them put in, for instance,

CA, NV, CO

and, in the code, check for a comma in the string and, based on that, create the full SQL statement.

For example:

If there is a comma:
Me.OracleSelectCommand1.CommandText = "SELECT authors FROM a WHERE state IN (" & :PARAM1 &") "

If there is no comma:
Me.OracleSelectCommand1.CommandText = "SELECT authors FROM a WHERE state = " & :PARAM1

Of course, you may need to adjust the actual phrasing of the code.

But how can I add parameter in code if I need to add unknown number of states?
Me.OracleSelectCommand1.Parameters.Add(":PARAM1", OracleType.VarChar, 255, "state"))
The Add.Value should be "CA", "NV", "CO" respectively, not a whole string.

Thanks.

Let me clarify a bit here:

I had used the ":Param1" as, in effect a place holder and not as an actual SQL parameter. Let's assume that the text field where the user enters the stae or states is "YourField", then you would actually code something like:

If there is a comma:
Me.OracleSelectCommand1.CommandText = "SELECT authors FROM a WHERE state IN (" & YourField.text &") "

If there is no comma:
Me.OracleSelectCommand1.CommandText = "SELECT authors FROM a WHERE state = " & YourField.text

In other words, build the whole SQL statement in yoru code. Admittedly, this is a little less efficient than using a parameterized SQL statement but there comes a time when one sacrifices absolute effeiciency for "works good enough and is easier to code".