How To Create Temporary Table inside a function

hi everyone ,
how can i create temp table say table1 with three column of types varchar , int and int, inside the function body and if that same table already exist it should drop that already existing table(table1) , and on every run this process should run. and how can i insert values from postgresql view say vwfirst to this table(table1)

Here is the MS-SQL code for this process but  i want to know how can this be done in postgresql

if object_id('tempdb..#tblTFSites1') is not null
  drop table tempdb..#tblTFSites1

create table #tblTFSites1(
Chr varchar(50) NULL,
Start int NULL,
[End] int NULL
)

INSERTION PROCESS

INSERT INTO #tblTFSites1 (Chr, Start,[End])
Select Chr_U, Start_U, End_U from vwChrCompareSites where KBId=(at)ID and UserDataDetailId=(at)UserDataDetailId 
and bpOverlap >= @bpOverlap and (CentreDistance <= @CentreDistance or @CentreDistance=1)