[PERFORM] Optimization inner join

Hi,

Is there something in the roadmap to optimize the inner join?

I've this situation above. Table b has 400 rows with null in the column b.

explain analyze select * from a inner join b on (b.b = a.a);

"Merge Join  (cost=0.55..65.30 rows=599 width=16) (actual time=0.030..1.173 rows=599 loops=1)" 
"  Merge Cond: (a.a = b.b)" 
"  ->  Index Scan using a_pkey on a  (cost=0.28..35.27 rows=1000 width=8) (actual time=0.014..0.364 rows=1000 loops=1)" 
"  ->  Index Scan using in01 on b  (cost=0.28..33.27 rows=1000 width=8) (actual time=0.012..0.249 rows=600 loops=1)" 
"Total runtime: 1.248 ms" 

My question is: Why the planner isn't removing the null rows during the scan of table b?

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Clailson Soares Dinízio de Almeida