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help / color / mirror / Atom feedFrom: Jian He <[email protected]>
To: pgsql-sql <[email protected]>
Subject: Histogram question.
Date: Tue, 5 Apr 2022 20:04:44 +0530
Message-ID: <CAMV54g17LBTqs069dE5c1EmnGnJXmMtgCNxH5vesjfbJY8_D0g@mail.gmail.com> (raw)
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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