Goal Find pairs of non-function based unique indexes that cover the same set of columns. Include indexes that support a constraint (primary key, unique, exclude), i.e., these indexes have been automatically created due to the constraint declaration. For instance, it helps us to find unique indexes that have been defined to already unique columns.
Notes The query does not take into account the order of colums in the index, i.e., indexes (a, b) and (b, a) are considered duplicates.
Type Problem detection (Each row in the result could represent a flaw in the design)
Reliability High (Few or no false-positive results)
License MIT License
Fixing Suggestion Drop the duplicates. Do not drop the duplicate that supports a constraint but a duplicate that is user-defined.
Data Source system catalog only
SQL Query
WITH indexes AS (SELECT 
  n.nspname AS sch,
  c2.relname AS tbl,
  c.relname AS indx,    
  string_agg(a.attname, ',' ORDER BY a.attname) AS clm,
  EXISTS (SELECT * FROM pg_catalog.pg_constraint AS o WHERE o.conindid=i.indexrelid) AS is_constraint
FROM 
  pg_catalog.pg_class AS c INNER JOIN pg_catalog.pg_index AS i ON i.indexrelid = c.oid
  INNER JOIN pg_catalog.pg_class AS c2  ON i.indrelid = c2.oid
  INNER JOIN pg_catalog.pg_namespace AS n ON c.relnamespace = n.oid
  INNER JOIN pg_catalog.pg_authid AS u ON  n.nspowner = u.oid
  INNER JOIN pg_catalog.pg_attribute AS a ON a.attrelid = c.oid    
WHERE c.relkind = 'i'
AND i.indexprs IS NULL
AND i.indisunique=TRUE
AND a.attnum>=1
AND a.attisdropped = FALSE
AND (n.nspname = 'public'
	 OR u.rolname <> 'postgres')
GROUP BY n.nspname, c2.relname, c.relname, i.indisunique, is_constraint)
SELECT A.sch AS table_schema, A.tbl AS table_name, A.is_constraint AS is_idx1_constraint, A.indx AS idx1, A.clm AS idx1_columns,
B.clm AS idx2_columns, B.is_constraint AS is_idx2_constraint, B.indx AS idx2
FROM indexes AS A, indexes AS B
WHERE A.sch=B.sch 
AND A.tbl=B.tbl 
AND A.indx>B.indx
AND a.clm=b.clm
ORDER BY A.sch, A.tbl, A.indx, B.indx;

Collections

This query belongs to the following collections:

NameDescription
Find problems about integrity constraintsA selection of queries that return information about the state of integrity constraints in the datadabase. Contains all the types of queries - problem detection, software measure, and general overview
Find problems automaticallyQueries, that results point to problems in the database. Each query in the collection produces an initial assessment. However, a human reviewer has the final say as to whether there is a problem or not .
Categories

This query is classified under the following categories:

NameDescription
PerformanceQueries of this category provide information about indexes in a database.
UniquenessQueries of this category provide information about uniqueness constraints (PRIMARY KEY, UNIQUE, EXCLUDE) as well as unique indexes.