Goal Find cases where two candidate keys of the same table that are also foreign keys reference to each other.
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 Redesign the database to remove the cycle.
Data Source system catalog only
SQL Query
with fk as (select
o.conname,
(select nspname from pg_namespace where oid=f.relnamespace) as foreign_schema,
f.relname as foreign_table,
f.oid as foreign_table_oid,
o.confkey AS foreign_col,
(select nspname from pg_namespace where oid=c.relnamespace) as target_schema,
c.relname as target_table,
c.oid as target_table_oid,
o.conkey AS target_col
from pg_constraint o inner join pg_class c on c.oid = o.conrelid
inner join pg_class f on f.oid = o.confrelid
where o.contype = 'f'),
fk_unnest as (select conname, foreign_schema, foreign_table,  foreign_table_oid, foreign_col, foreign_col_num, target_schema, target_table, target_table_oid, target_col, target_col_num, ordin
from fk, unnest(fk.foreign_col, fk. target_col) with ordinality as f(foreign_col_num, target_col_num, ordin)),
fk_with_names as (select conname, foreign_schema, foreign_table, array_agg(a_foreign.attname order by ordin) as foreign_col, target_schema, target_table, array_agg(a_target.attname order by ordin) as target_col
from fk_unnest fk inner join pg_attribute a_foreign on fk.foreign_col_num = a_foreign.attnum and fk.foreign_table_oid = a_foreign.attrelid and a_foreign.attisdropped = false
inner join pg_attribute a_target on fk.target_col_num = a_target.attnum and fk.target_table_oid = a_target.attrelid and a_target.attisdropped = false
group by conname, foreign_schema, foreign_table, target_schema, target_table),
intersection as (select foreign_schema, foreign_table, foreign_col, target_schema, target_table, target_col
from fk_with_names
intersect select target_schema, target_table, target_col, foreign_schema, foreign_table, foreign_col
from fk_with_names)
select  target_schema, target_table, target_col, foreign_schema, foreign_table, foreign_col
from intersection
where foreign_col<>target_col
and foreign_schema=target_schema
and foreign_table=target_table
order by target_schema, target_table;

Collections

This query belongs to the following collections:

NameDescription
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
Relationships between tablesQueries of this category provide information about how database tables are connected to each other and whether such connections have been explicitly defined and whether it has been done correctly.