Declaring variables and select statement in a procedure - sql

Question

I'm writing a SQL procedure which should use calculated date stored as a local variable in a select statement. I'm using Oracle SQL developer. My code is:
create or replace PROCEDURE
my_procedure
AS
BEGIN
DECLARE
l_max_dt DATE;
BEGIN
SELECT MAX(TRX_DT)
INTO l_max_dt
FROM TABLE
WHERE 1=1;
end;
select * from TABLE where trx_dt = l_max_dt;
end;
This code gives me an error : " Error(14,48): PL/SQL: ORA-00904: "L_MAX_DT": invalid identifier" when select statement is present.
How can I store variables to use them in statements?

Answer 1

This is how you write a Procedure. Syntax is incorrect. Read about syntax Here
CREATE OR REPLACE PROCEDURE my_procedure
AS
l_max_dt DATE;
v_var TABLE2%ROWTYPE;
BEGIN
SELECT MAX (TRX_DT)
INTO l_max_dt
FROM TABLE1
WHERE 1 = 1;
-- Assuming the query will retrun only 1 row.
SELECT *
INTO v_var
FROM TABLE2
WHERE trx_dt = l_max_dt;
END;

Answer 2

Your issue is one of scope. In your procedure, you have a nested block, in which you declare the l_max_dt variable. Once the code has exited that block, the l_max_dt variable is no longer in scope - i.e. the outer block does not know anything about it.
There is no need to have a nested block in this instance - you can do it all in the same block, like so:
create or replace PROCEDURE my_procedure
AS
l_max_dt DATE;
BEGIN
SELECT MAX(TRX_DT)
INTO l_max_dt
FROM TABLE
WHERE 1=1;
-- commented out as this isn't valid syntax; there is a missing INTO clause
-- select *
-- from TABLE where trx_dt = l_max_dt;
END my_procedure;
However, you could simply do the query in one fell swoop - e.g.:
select *
from your_table
where trx_dt = (select max(trx_dt) from your_table);
A couple of points about your procedure:
In PL/SQL, if you use an implicit cursor (i.e. when you put a select statement directly in the body of the code) you need to have something to put the results into. You could bulk collect the results into an array, or you could ensure that you will receive exactly one row (or code error handling for NO_DATA_FOUND and TOO_MANY_ROWS) into a record or corresponding scalar variables.
You shouldn't use select * in your procedure - instead, you should explicitly state the columns being returned, because someone adding a column to that table could cause your procedure to error. There are exceptions to this "rule", but explicitly stating the columns is a good habit to get into.