In Microsoft SQL Server, to test something like this in the query window:

```
select * from Users where LastName = @lastname

```

I can add this before the command:

```
declare @lastname varchar(16)
set @lastname = 'Troy'

```

But in PostgreSQL, I cannot find a similar way to do so. It seems the only thing I can do is to replace the parameter name directly with its value. It gets hard when the ad-hoc query gets complicated and the same parameter gets used several times. Is there a way?