What is the simplest way to define a local variable in Oracle?

Question

In the SQL Server, I can define local variables like this.

declare @id number := 1000

select * from tbl_A where id = @id;
select * from tbl_B where id = @id;

It is very convenient. I tried to do same thing in PL/SQL but it doesn't work.

DECLARE id number;
select 1000 into id from dual;

Do you know how to do something similar? The simplest method is my objective.

Solution 1

If you want to define a local variable in PL/SQL, you need a complete PL/SQL block

DECLARE
  id NUMBER;
BEGIN
  SELECT 1000
    INTO id
    FROM dual;
END;

or just

DECLARE
  id NUMBER := 1000;
BEGIN
  <<do something that uses the local variable>>
END;

If you want to declare a variable in SQL*Plus

SQL> variable id number
SQL> begin
       select 1000 into :id from dual;
     end;
     /

SQL> print id

        ID
----------
      1000

SQL> SELECT * FROM tbl_a WHERE id = :id

Solution 2

Solution for Oracle SQL

DEF x = foo
SELECT '&x' FROM dual;

The result will be : foo

NB: The variable will keep the value even after execution. To clear variable run UNDEFINE x.

Solution 3

An alternative to DECLARE Block is to use a WITH Clause:

WITH my_params AS (
    SELECT 123 AS min_id FROM DUAL
) 
SELECT * 
FROM some_table 
WHERE id > (SELECT min_id FROM my_params)

It is more portable as many vendors support the WITH clause and you can change seamless from parameter to dynamic value. For example:

WITH my_params AS (
    SELECT min(id) AS min_id FROM some_id_table
) 
SELECT * 
FROM some_table 
WHERE id > (SELECT min_id FROM my_params)