Foreign key constraint references to the columns of a UNIQUE constraint not to the columns of the PRIMARY KEY constraint

with unique_keys as (select 
o.conname, 
(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
where o.contype ='u'),
unique_keys_unnest as (select target_schema, target_table, target_table_oid, target_col, target_col_num, ordin
from unique_keys, unnest(unique_keys. Target_col) with ordinality as f(target_col_num, ordin)),
unique_keys_with_names as (select target_schema, target_table, array_agg(a_target.attname order by a_target.attname) as key_columns
from unique_keys_unnest k inner join  pg_attribute a_target on k.target_col_num = a_target.attnum and k.target_table_oid = a_target.attrelid and a_target.attisdropped = false
group by target_schema, target_table),
unique_keys_with_names_agg as (select  target_schema, target_table, key_columns
from unique_keys_with_names),
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)
select f.conname, f.foreign_schema, f.foreign_table, f.foreign_col, f.target_schema, f.target_table, f.target_col
from fk_with_names as f inner join unique_keys_with_names_agg as u on  f.foreign_schema=u.target_schema and f.foreign_table=u.target_table and f.foreign_col=u.key_columns
order by target_schema, target_table, conname;

Query goal:	Find foreign key constraints that reference to a UNIQUE constraint columns not to the PRIMARY KEY constraint columns. This is legal in SQL. However, a tradition is to refer to the primary key columns. If most of the foreign keys refer to the primary key columns, then it raises a question as to whether this kind of design decision has a good reason in a particular case or whether it is an inconsistency.
Query type:	Problem detection (Each row in the result could represent a flaw in the design)
Query reliability:	High (Few or no false-positive results)
Query license:	MIT License
Data source:	system catalog only
SQL query:	Click on query to copy it with unique_keys as (select o.conname, (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 where o.contype ='u'), unique_keys_unnest as (select target_schema, target_table, target_table_oid, target_col, target_col_num, ordin from unique_keys, unnest(unique_keys. Target_col) with ordinality as f(target_col_num, ordin)), unique_keys_with_names as (select target_schema, target_table, array_agg(a_target.attname order by a_target.attname) as key_columns from unique_keys_unnest k inner join pg_attribute a_target on k.target_col_num = a_target.attnum and k.target_table_oid = a_target.attrelid and a_target.attisdropped = false group by target_schema, target_table), unique_keys_with_names_agg as (select target_schema, target_table, key_columns from unique_keys_with_names), 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) select f.conname, f.foreign_schema, f.foreign_table, f.foreign_col, f.target_schema, f.target_table, f.target_col from fk_with_names as f inner join unique_keys_with_names_agg as u on f.foreign_schema=u.target_schema and f.foreign_table=u.target_table and f.foreign_col=u.key_columns order by target_schema, target_table, conname;

Collection name	Collection description
Find problems about integrity constraints	A 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 automatically	Queries, 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 .

Category name	Category description
Inconsistencies	Queries of this catergory provide information about inconsistencies of solving the same problem in different places.
Relationships between tables	Queries 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.
Uniqueness	Queries of this category provide information about uniqueness constraints (PRIMARY KEY, UNIQUE, EXCLUDE) as well as unique indexes.

Foreign key constraint references to the columns of a UNIQUE constraint not to the columns of the PRIMARY KEY constraint

Collections where the query belongs to

Categories where the query belongs to

Reference materials for further reading

Reference
The corresponding code smell in case of cleaning code is "G11: Inconsistency". (Robert C. Martin, Clean Code)
Based on rule 2 in: Delplanque, J., Etien, A., Auverlot, O., Mens, T., Anquetil, N., Ducasse, S.: CodeCritics applied to database schema: Challenges and first results. In: 2017 IEEE 24th International Conference on Software Analysis, Evolution and Reengineering (SANER), pp. 432-436. IEEE, (2017).