Alias same with column name

alias.sql

CREATE TABLE test (a int, b text);

EXPLAIN (ANALYZE, VERBOSE) 
SELECT
	a,
	case when b = '1' then '-' 
		 when b is null then '-' 
	else b end as b,
	count(*)
FROM 
	test
GROUP BY a, b;
                                                   QUERY PLAN                                                   
----------------------------------------------------------------------------------------------------------------
 HashAggregate  (cost=32.23..34.73 rows=200 width=76) (actual time=0.006..0.006 rows=0 loops=1)
   Output: a, CASE WHEN (b = '1'::text) THEN '-'::text WHEN (b IS NULL) THEN '-'::text ELSE b END, count(*), b
   Group Key: test.a, test.b
   ->  Seq Scan on public.test  (cost=0.00..22.70 rows=1270 width=36) (actual time=0.004..0.004 rows=0 loops=1)
         Output: a, b
 Planning Time: 0.726 ms
 Execution Time: 0.065 ms
(7 rows)

Time: 2.074 ms



-- now, same query on distributed tables
SELECT create_distributed_table('test', 'a');
EXPLAIN (ANALYZE, VERBOSE) 
SELECT
	a,
	case when b = '1' then '-' 
		 when b is null then '-' 
	else b end as b,
	count(*)
FROM 
	test
GROUP BY a, b;

                                                               QUERY PLAN                                                               
----------------------------------------------------------------------------------------------------------------------------------------
 Custom Scan (Citus Adaptive)  (cost=0.00..0.00 rows=100000 width=76) (actual time=29.075..29.079 rows=0 loops=1)
   Output: remote_scan.a, remote_scan.b, remote_scan.count, remote_scan.worker_column_4
   Task Count: 32
   Tasks Shown: One of 32
   ->  Task
         Node: host=localhost port=9700 dbname=postgres
         ->  HashAggregate  (cost=32.23..34.73 rows=200 width=76) (actual time=0.008..0.008 rows=0 loops=1)
               Output: a, CASE WHEN (b = '1'::text) THEN '-'::text WHEN (b IS NULL) THEN '-'::text ELSE b END, count(*), b
               Group Key: test.a, test.b
               ->  Seq Scan on public.test_102074 test  (cost=0.00..22.70 rows=1270 width=36) (actual time=0.007..0.007 rows=0 loops=1)
                     Output: a, b
             Planning Time: 0.100 ms
             Execution Time: 0.045 ms
 Planning Time: 1.822 ms
 Execution Time: 29.103 ms
(15 rows)

Time: 35.042 ms