Simple use of variables in query

Question

Hi,
i've just started using PL/SQL and as a long time user of TSQL the syntax is a bit confusing for me. I'm trying to test a simple query - using a variable to select some rows from a table. Lest assume that we have a table with data from different days and we want to view data from specific day.
I could use:
SELECT * FROM TABLE
where TRADE_DATE = '2010-10-23'
but what i would like to do is to pass the date value as a variable, in TSQL i'd just write:
declare @trade_date datetime
set @trade_date = '2010-10-23'
SELECT * FROM TABLE
where TRADE_DATE = @trade_date
Could someone help me and write the last query using PL/SQL syntax?
Also - it there some kind of a tutorial for people like me? comparison of simple queries written in both languages? tried to google it but didn't have luck.

Answer 1

There are a couple of differences besides variable syntax. The variable would look like this in PL/SQL:
declare
    v_trade_date date := DATE '2010-10-23';
begin
    select * into ?????  -- see below
    from   table
    where  trade_date = v_trade_date;
end;However the next difference is that PL/SQL does not implicitly return result sets to the client application, so you either have to select <b>into</b> a PL/SQL variable, or process the values in a loop, or explicitly return a ref cursor (or just do the processing in SQL statements within the procedure, without returning anything). I don't know much about T-SQL but I have the impression that in Oracle there is a stronger distinction between SQL (the interpreted query language) and PL/SQL (the compiled programming language) than the equivalents in SQL Server. Saubhik's example above is not PL/SQL (which you asked about) but plain SQL.
Using the example of SQL*Plus, you might use a ref cursor like this:
var r refcursor;
declare
    v_trade_date date := DATE '2010-10-23';
begin
    open :r for
    select *
    from   test_table
    where  trade_date = v_trade_date;
end;
print :ror
var r refcursor;
create or replace procedure p (p_out_results out sys_refcursor)
as
    v_trade_date date := DATE '2010-10-23';
begin
    open p_out_results for
    select *
    from   test_table
    where  trade_date = v_trade_date;
end p;
set autoprint on
exec p(:r)Edited by: William Robertson on Oct 24, 2010 5:31 PM