Oracle variables

Question

Hi:
I want to run a statement similar to this
DEFINE MaxDate;
MaxDate := SELECT Max(dtDateField) FROM myTable;
SELECT * FROM myTable2 WHERE dtDateField < MaxDate;
This is not correct obviously--how do I set a variable to the value of a SELECT statement? I've tried different ways and what I've read just seems to talk about using a variable to set a constant value.
Thanks,
Kayda

Answer 1

> So you are saying there is no way of doing this with
variables? I want to reuse the variables in many
statements (actually using in UPDATES) so it makes
sense to do this calculation once only. Any way to do
this?
In what language? The SQL language does not support normal variables like Delphi, Visual Basic, C#, Java, etc.
The variables supported in SQL is called bind variables. These are position/place holders for values that you (the caller of the SQL) must supply at run-time.
For example, the following is a SQL "program" (aka statement) that is parsed and compiled by the SQL Engine, and stored for re-use:
SELECT SUM(amount) FROM invoice_lines WHERE invoice_id = :0
The :0 is a bind variable. This SQL "program" can be used by you and me and others repeatedly - for different invoices. We (the callers) simply need to supply a value for the invoice id bind variable.
If you want to store the amount returned by the SQL "program" as a variable.. that is your problem. Not the SQL Engine's problem. It does not deal with variables that way.
You need to define a variable. You need to fetch the value (result) from the SQL "program" and store it.
In PL/SQL (a formal procedural programming language like Delphi and C), you can do it as follows:
declare
invAmount number;
invID number := 1234;
begin
select SUM(amount) into invAmount from invoice_lines
where invoice_id = invID;
end;There is thus no such thing as Oracle Variables.