From: | Jian He <hejian(dot)mark(at)gmail(dot)com> |
---|---|
To: | pgsql-sql <pgsql-sql(at)lists(dot)postgresql(dot)org> |
Subject: | Histogram question. |
Date: | 2022-04-05 14:34:44 |
Message-ID: | CAMV54g17LBTqs069dE5c1EmnGnJXmMtgCNxH5vesjfbJY8_D0g@mail.gmail.com |
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Lists: | pgsql-sql |
Queries in PostgreSQL: 2. Statistics : Postgres Professional
<https://postgrespro.com/blog/pgsql/5969296>
SELECT sum(s.most_common_freqs[ array_position((s.most_common_vals::text::
text[]),v) ]) FROM pg_stats s, unnest(s.most_common_vals::text::text[]) v
WHERE s.tablename = 'boarding_passes' AND s.attname = 'seat_no';
*return 0.6762. *
SELECT sum(s.most_common_freqs[ array_position((s.most_common_vals::text::
text[]),v) ]) FROM pg_stats s, unnest(s.most_common_vals::text::text[]) v
WHERE s.tablename = 'boarding_passes' AND s.attname = 'seat_no' AND v >
'30C';
return *0.2127*
SELECT round( reltuples * ( 0.2127 -- from most common values + (1 - 0.6762
- 0) * (49 / 100.0) -- from histogram )) FROM pg_class WHERE relname =
'boarding_passes';
the above mentioned query, the part I don't understand is *49/100.*
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