How to debug efficiently

Hi All

In SQL Server I could copy sql code out of an application and paste it into
SSMS, declare & assign vars that exist in the sql and run.. yay great
debugging scenario.

e.g. (please note I am rusty and syntax may be incorrect)

declare @x as varchar(10)
set @x = 'abc'
select * from sometable where somefield = @x

I want to do something simular with postgres in pgadmin3 (or another
postgres tool, anyy reccomendations?)

I realise you can create pgscript, but it doesn't appear to be very good,
for example, if I do the equlivent of above, it doesn't put the single
quotes around the value in @x, nor does it let me by doubling them up and
you don't get a table out after - only text...

Currently I have a peice of sql someone has written that has 3 unique
varibles in it which are used around 6 times each...

So the question is how do other people debug sql this sql EFFICIENTLY,
preferably in a simular fashion to my sql server days.

Regards

Dan