Re: Unable to understand index only scan as it is not happening for one table while it happens for other

Ah! Got it. Thanks. One more question,

why the index-only scan *works only* with an *order by*?
localdb=# explain analyse verbose select uid from mm where uid>100 *order
by* uid;
QUERY
PLAN
---------------------------------------------------------------------------------------------------------------------------------------------------
Index Only Scan using mm_pkey on public.mm (cost=0.27..22.47 rows=354
width=8) (actual time=0.023..0.079 rows=354 loops=1)
Output: uid
Index Cond: (mm.uid > 100)
Heap Fetches: 0
Planning time: 0.096 ms
Execution time: 0.131 ms
(6 rows)

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Thanks,
Rajan.
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