From 619dc7fac8d8ee57d0fef83fae0ee6b102e9bf14 Mon Sep 17 00:00:00 2001
From: Tomas Vondra <tomas@2ndquadrant.com>
Date: Thu, 13 Jun 2019 17:25:04 +0200
Subject: [PATCH 2/2] Add pg_stats_ext view

Introduces a view on top of pg_statistic_ext and pg_statistic_ext_data,
showing data in a way that is easier to read for humans. This is similar
to what pg_stats does for pg_statistic.
---
 src/backend/catalog/system_views.sql | 41 ++++++++++++++++++++++++++++
 src/test/regress/expected/rules.out  | 29 ++++++++++++++++++++
 2 files changed, 70 insertions(+)

diff --git a/src/backend/catalog/system_views.sql b/src/backend/catalog/system_views.sql
index 78a103cdb9..c889890118 100644
--- a/src/backend/catalog/system_views.sql
+++ b/src/backend/catalog/system_views.sql
@@ -253,6 +253,47 @@ CREATE VIEW pg_stats WITH (security_barrier) AS
 
 REVOKE ALL on pg_statistic FROM public;
 
+CREATE VIEW pg_stats_ext WITH (security_barrier) AS
+    SELECT cn.nspname AS schemaname,
+           c.relname AS tablename,
+           sn.nspname AS statistics_schemaname,
+           s.stxname AS statistics_name,
+           pg_get_userbyid(s.stxowner) AS statistics_owner,
+           ( SELECT array_agg(a.attname ORDER BY a.attnum)
+             FROM unnest(s.stxkeys) k
+                  JOIN pg_attribute a
+                       ON (a.attrelid = s.stxrelid AND a.attnum = k)
+           ) AS attnames,
+           s.stxkind AS kinds,
+           sd.stxdndistinct AS n_distinct,
+           sd.stxddependencies AS dependencies,
+           m.most_common_vals,
+           m.most_common_val_nulls,
+           m.most_common_freqs,
+           m.most_common_base_freqs
+    FROM pg_statistic_ext s JOIN pg_class c ON (c.oid = s.stxrelid)
+         JOIN pg_statistic_ext_data sd ON (s.oid = sd.stxoid)
+         LEFT JOIN pg_namespace cn ON (cn.oid = c.relnamespace)
+         LEFT JOIN pg_namespace sn ON (sn.oid = s.stxnamespace)
+         LEFT JOIN LATERAL
+                   ( SELECT array_agg(values) AS most_common_vals,
+                            array_agg(nulls) AS most_common_val_nulls,
+                            array_agg(frequency) AS most_common_freqs,
+                            array_agg(base_frequency) AS most_common_base_freqs
+                     FROM pg_mcv_list_items(sd.stxdmcv)
+                   ) m ON sd.stxdmcv IS NOT NULL
+    WHERE NOT EXISTS
+              ( SELECT 1
+                FROM unnest(stxkeys) k
+                     JOIN pg_attribute a
+                          ON (a.attrelid = s.stxrelid AND a.attnum = k)
+                WHERE NOT has_column_privilege(c.oid, a.attnum, 'select') )
+    AND (c.relrowsecurity = false OR NOT row_security_active(c.oid));
+
+REVOKE ALL on pg_statistic_ext FROM public;
+GRANT SELECT (oid, stxrelid, stxname, stxnamespace, stxowner, stxkeys, stxkind)
+    ON pg_statistic_ext TO public;
+
 CREATE VIEW pg_publication_tables AS
     SELECT
         P.pubname AS pubname,
diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out
index 7d365c48d1..210e9cd146 100644
--- a/src/test/regress/expected/rules.out
+++ b/src/test/regress/expected/rules.out
@@ -2284,6 +2284,35 @@ pg_stats| SELECT n.nspname AS schemaname,
      JOIN pg_attribute a ON (((c.oid = a.attrelid) AND (a.attnum = s.staattnum))))
      LEFT JOIN pg_namespace n ON ((n.oid = c.relnamespace)))
   WHERE ((NOT a.attisdropped) AND has_column_privilege(c.oid, a.attnum, 'select'::text) AND ((c.relrowsecurity = false) OR (NOT row_security_active(c.oid))));
+pg_stats_ext| SELECT cn.nspname AS schemaname,
+    c.relname AS tablename,
+    sn.nspname AS statistics_schemaname,
+    s.stxname AS statistics_name,
+    pg_get_userbyid(s.stxowner) AS statistics_owner,
+    ( SELECT array_agg(a.attname ORDER BY a.attnum) AS array_agg
+           FROM (unnest(s.stxkeys) k(k)
+             JOIN pg_attribute a ON (((a.attrelid = s.stxrelid) AND (a.attnum = k.k))))) AS attnames,
+    s.stxkind AS kinds,
+    sd.stxdndistinct AS n_distinct,
+    sd.stxddependencies AS dependencies,
+    m.most_common_vals,
+    m.most_common_val_nulls,
+    m.most_common_freqs,
+    m.most_common_base_freqs
+   FROM (((((pg_statistic_ext s
+     JOIN pg_class c ON ((c.oid = s.stxrelid)))
+     JOIN pg_statistic_ext_data sd ON ((s.oid = sd.stxoid)))
+     LEFT JOIN pg_namespace cn ON ((cn.oid = c.relnamespace)))
+     LEFT JOIN pg_namespace sn ON ((sn.oid = s.stxnamespace)))
+     LEFT JOIN LATERAL ( SELECT array_agg(pg_mcv_list_items."values") AS most_common_vals,
+            array_agg(pg_mcv_list_items.nulls) AS most_common_val_nulls,
+            array_agg(pg_mcv_list_items.frequency) AS most_common_freqs,
+            array_agg(pg_mcv_list_items.base_frequency) AS most_common_base_freqs
+           FROM pg_mcv_list_items(sd.stxdmcv) pg_mcv_list_items(index, "values", nulls, frequency, base_frequency)) m ON ((sd.stxdmcv IS NOT NULL)))
+  WHERE ((NOT (EXISTS ( SELECT 1
+           FROM (unnest(s.stxkeys) k(k)
+             JOIN pg_attribute a ON (((a.attrelid = s.stxrelid) AND (a.attnum = k.k))))
+          WHERE (NOT has_column_privilege(c.oid, a.attnum, 'select'::text))))) AND ((c.relrowsecurity = false) OR (NOT row_security_active(c.oid))));
 pg_tables| SELECT n.nspname AS schemaname,
     c.relname AS tablename,
     pg_get_userbyid(c.relowner) AS tableowner,
-- 
2.20.1