Using an Oracle database (currently 18g) through dbVisualizer, I have SQL that has parameters peppered throughout. Some of the parameters are in multiple places. The query I'm working with right now has 13 distinct parameter names with 56 total references in the code. I have some standard values I use for testing. I don't want to use the interface dbVisualizer presents for entering them manually. I want to use a text editor to enter my test values and put them all at the beginning of my code so I don't risk fat-fingering my SQL logic and so I can delete or comment out that section when I'm done testing.
I've done this for decades in SQL Server...
declare @varname varchar(50)
set @varname = 'asdf'
select @varname
...but I don't see a way to do this in Oracle. I have read many posts regarding how to do this using PL/SQL or SQL*Plus (like https://dba.stackexchange.com/questions/3652/how-do-i-declare-and-use-variables-in-oracle) that don't work for my environment. I have also seen posts with accepted answers that just don't work (like Declare a variable in Oracle SQL to use in a query).
How can I declare variables in Oracle SQL through dbVisualizer as easily as I can in SQL Server using SSMS?