SQL Syntax - help needed

Question

Guys,
Help me understand the syntax please!! With PL/SQL I have achieved a task quite easily, with a branch of code to include or exclude some part of the query - no problem. But to use SQL ......
If i have a variable on a page, say :p10_open_or_closed
.. and I set the value of this to the text "Is Not Null"
How can I incorporate this into an SQL query, say
Select ID, Date1, Date2, Comment
From Table1
where Date1 Is Not Null
Is there a way of substituting the ":p10_open_or_closed" variable into this query?
ie
Select ID, Date1, Date2, Comment
From Table1
where Date1 ":p10_open_or_closed"
Thanks.

Answer 1

Thanks for your help gents.
Originally, I had a PL/SQL Statement constructing the code as needed, as Rekha
suggested.
if :P1_OPEN_OR_CLOSED = 1 then
q:=q||' and ';
q:=q||' p.ACTUAL_INSTALL_DATE is null ';
end if;
if :P1_OPEN_OR_CLOSED = 2 then
q:=q||' and ';
q:=q||' p.ACTUAL_INSTALL_DATE is not null ';
end if;
But, to use a Tabular form, where users can update fields of multiple records on screen then submit for a MRU, the option of PL/SQL code is not allowed, only SQL. So Phil UK, no it's not an elegant way of doing things, but I'm forced to use SQL, yeah?
There are definitely ways that I can filter for the solution I am after, but they all involve more in depth solutions (that are not that great). Thus, I asked at this forum.
Andy, your solution works :~) which makes me very happy. I'm not sure how just now but I'll learn from it.
Thanks again.