This query identifies base tables with a potentially redundant key structure, specifically those having more than one PRIMARY KEY or UNIQUE constraint defined on a single integer-type column. This pattern may suggest the presence of multiple surrogate keys for the same entity, which can indicate overcomplicated data model. A single entity should typically have only one system-generated identifier to maintain schema clarity, simplify join logic, and avoid redundancy. The presence of multiple such keys warrants a review to determine if one is superfluous.
Notes
In case of the string_agg function, the line break (br) tag is used as a part of the separator for the better readability in case the query result is displayed in a web browser.
Type
Problem detection (Each row in the result could represent a flaw in the design)
with simple_keys as (select
n.nspname as table_schema,
c.relname as table_name,
(SELECT a.attname FROM pg_attribute a WHERE a.attrelid = c.oid AND a.attnum = o.conkey[1] AND a.attisdropped = FALSE) AS column_name
from pg_constraint o inner join pg_class c on c.oid = o.conrelid
inner join pg_namespace n on c.relnamespace=n.oid
where o.contype in ('u', 'p')
and c.relkind = 'r'
and cardinality(o.conkey)=1
and n.nspname NOT IN (SELECT schema_name
FROM INFORMATION_SCHEMA.schemata
WHERE schema_name<>'public' AND
schema_owner='postgres' AND schema_name IS NOT NULL)),
integer_columns AS (SELECT table_schema, table_name, column_name
FROM INFORMATION_SCHEMA.columns
WHERE data_type IN ('smallint', 'integer', 'bigint')
AND (table_schema, table_name) IN (SELECT table_schema, table_name
FROM INFORMATION_SCHEMA.tables
WHERE table_type IN ('BASE TABLE'))
AND 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))
SELECT table_schema, table_name, Count(*) AS number_of_simple_int_keys, string_agg (column_name, '; ' ORDER BY column_name) AS simple_int_keys
FROM simple_keys
WHERE (table_schema, table_name, column_name) IN (SELECT table_schema, table_name, column_name
FROM integer_columns)
GROUP BY table_schema, table_name
HAVING Count(*) >1
ORDER BY Count(*) DESC, table_schema, table_name;
Categories
This query is classified under the following categories:
Name
Description
Duplication of implementation elements
Queries of this catergory provide information about the duplication of the database objects.
Uniqueness
Queries of this category provide information about uniqueness constraints (PRIMARY KEY, UNIQUE, EXCLUDE) as well as unique indexes.
Validity and completeness
Queries of this category provide information about whether database design represents the world (domain) correctly (validity) and whether database design captures all the information about the world (domain) that is correct and relevant (completeness).