Goal Find statistics about how many base tables have how many derived tables that use these tables.
Type Sofware measure (Numeric values (software measures) about the database)
License MIT License
Data Source INFORMATION_SCHEMA+system catalog
SQL Query
WITH derived_tables AS (SELECT t.table_schema, t.table_name, vtu.view_schema, vtu.view_name, 'VIEW' AS type
FROM 
  information_schema.tables AS t INNER JOIN information_schema.view_table_usage AS vtu
ON
  t.table_schema = vtu.table_schema AND
  t.table_name = vtu.table_name
WHERE t.table_type = 'BASE TABLE' AND t.table_schema NOT IN (SELECT schema_name
FROM INFORMATION_SCHEMA.schemata
WHERE schema_name<>'public' AND
schema_owner='postgres' AND schema_name IS NOT NULL)
UNION SELECT DISTINCT 
source_ns.nspname as source_schema,
source_table.relname as source_table,
dependent_ns.nspname as dependent_schema,
dependent_view.relname as dependent_view,
'MATERIALIZED VIEW' AS type
FROM pg_depend 
JOIN pg_rewrite ON pg_depend.objid = pg_rewrite.oid 
JOIN pg_class as dependent_view ON pg_rewrite.ev_class = dependent_view.oid 
JOIN pg_class as source_table ON pg_depend.refobjid = source_table.oid 
JOIN pg_namespace dependent_ns ON dependent_ns.oid = dependent_view.relnamespace
JOIN pg_namespace source_ns ON source_ns.oid = source_table.relnamespace
WHERE dependent_view.relkind='m'
AND dependent_ns.nspname NOT IN (SELECT schema_name
FROM INFORMATION_SCHEMA.schemata
WHERE schema_name<>'public' AND 
schema_owner='postgres' AND schema_name IS NOT NULL) AND 
(dependent_ns.nspname ||'.'|| dependent_view.relname<>source_ns.nspname||'.'||source_table.relname)) ,
nr_of_using_views AS (SELECT Count(view_name) AS number_of_using_views
FROM derived_tables
WHERE view_name IS NOT NULL
GROUP BY table_schema, table_name)
SELECT number_of_using_views, Count(*) AS number_of_tables
FROM nr_of_using_views
GROUP BY number_of_using_views
ORDER BY number_of_tables DESC, number_of_using_views;

Collections

This query belongs to the following collections:

NameDescription
Find problems by overviewQueries that results point to different aspects of database that might have problems. A human reviewer has to decide based on the results as to whether there are problems or not .
Categories

This query is classified under the following categories:

NameDescription
Derived tablesQueries of this category provide information about the derived tables (views, materialized views), which are used to implement virtual data layer.