Before insert how to check the records if it exists or not

Question

hi,

 

I created two tables like

create Table A (pid bigint, pname varchar, psource varchar(10))

create Table #temp (id bigint, name varchar, source varchar(10))

table A having lakhs of rows and table #temp having lakhs of  rows

i want to check the records based on #temp table and insert into Table A.

how to check the records before insert values from #temp table to table A

insert into A

(pid,

pname,

psource

)

select

id,

name,

source

from #temp

Please give me the solution for the above query.