Inner join within Common Table Expression in PostgreSQL -

i have table "table1", contain following rows:

cola    colb -------------  p4      x1  p4      z  p4      z  p5      s  p5      t  p5      y1  p8      x1  p8      y1  p8      x1  p9      x1  p10     z1  p1      z1  p2      z1  p3      z1 

now need display table this:(as expected)

cola    colb    result ----------------------  p4      x1       0  p8      x1       0  p9      x1       0  p5      y1       0  p8      y1       0  p1      z1       0  p10     z1       0  p2      z1       0  p3      z1       0 

for writing query:

with cte  (     select colb,cola,dense_rank() over(partition colb order cola asc) tem     table1 ) select s.cola, s.colb, 0 result tem_table table1 s inner join cte c on c.colb = s.colb tem > 1 group s.cola,s.colb order s.colb; 

but dont want use inner join in above query because of low perfromance. trying query:

with cte  (     select colb,cola,dense_rank() over(partition colb order cola asc) tem     table1 )  select cola,colb,0 result tem_table cte tem > 1  group cola,colb  order colb; 

this gives output:(which not correct)

cola    colb    result ----------------------  p8      x1      0        p9      x1      0  p8      y1      0  p10     z1      0  p2      z1      0  p3      z1      0 

how can expected output without using inner join in cte because self joining getting more time execute.

select  cola, colb, 0    (         select  cola, colb, count(*) on (partition colb) cnt            (                 select  distinct cola, colb                    mytable                 ) q         ) q   cnt > 1