From 737f226842748cf946cad3bd30aadfd0c03ad16f Mon Sep 17 00:00:00 2001 From: Bruce Momjian Date: Mon, 30 Sep 2019 13:44:22 -0400 Subject: [PATCH] docs: adjust multi-column most-common-value statistics This commit adds a mention that the order of columns specified during multi-column most-common-value statistics is insignificant, and tries to simplify examples. Discussion: https://postgr.es/m/20190828162238.GA8360@momjian.us Backpatch-through: 12 --- doc/src/sgml/perform.sgml | 6 +++--- doc/src/sgml/ref/create_statistics.sgml | 3 ++- 2 files changed, 5 insertions(+), 4 deletions(-) diff --git a/doc/src/sgml/perform.sgml b/doc/src/sgml/perform.sgml index 763337b0e1..715aff63c8 100644 --- a/doc/src/sgml/perform.sgml +++ b/doc/src/sgml/perform.sgml @@ -1172,7 +1172,7 @@ WHERE tablename = 'road'; Here is an example of collecting functional-dependency statistics: -CREATE STATISTICS stts (dependencies) ON zip, city FROM zipcodes; +CREATE STATISTICS stts (dependencies) ON city, zip FROM zipcodes; ANALYZE zipcodes; @@ -1262,7 +1262,7 @@ SELECT * FROM zipcodes WHERE city = 'San Francisco' AND zip = '90210'; Continuing the previous example, the n-distinct counts in a table of ZIP codes might look like the following: -CREATE STATISTICS stts2 (ndistinct) ON zip, state, city FROM zipcodes; +CREATE STATISTICS stts2 (ndistinct) ON city, state, zip FROM zipcodes; ANALYZE zipcodes; @@ -1317,7 +1317,7 @@ nd | {"1, 2": 33178, "1, 5": 33178, "2, 5": 27435, "1, 2, 5": 33178} a function is required for inspection of MCV contents): -CREATE STATISTICS stts3 (mcv) ON state, city FROM zipcodes; +CREATE STATISTICS stts3 (mcv) ON city, state FROM zipcodes; ANALYZE zipcodes; diff --git a/doc/src/sgml/ref/create_statistics.sgml b/doc/src/sgml/ref/create_statistics.sgml index ec23a154d6..5b583aacb4 100644 --- a/doc/src/sgml/ref/create_statistics.sgml +++ b/doc/src/sgml/ref/create_statistics.sgml @@ -98,7 +98,8 @@ CREATE STATISTICS [ IF NOT EXISTS ] statistics_na The name of a table column to be covered by the computed statistics. - At least two column names must be given. + At least two column names must be given; the order of the column names + is insignificant.