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         


        

Answer 1

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)