Cycle in a hierarchy

Query goal:

There should not be cycles in hierarchies meaning that the parent must always be specified. In this case a parent must reference to a child or to itself, otherwise it cannot be registered.

Notes about the query:

Find implementations of the adjacency list pattern where the foreign key columns are mandatory. In this case each parent must also have a parent. Because there cannot be infinite amount of parents it means that some parent should have one of its child as a parent. The query excludes (based on table and column names) foreign key constraints on tables of users, persons etc that reference to the user who has registered, modified, or deleted the row. The query considers both column names in English and Estonian.

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

Fixing suggestion:

Drop the NOT NULL constraint of the foreign key columns that refer to a candidate key of the same table.

Data source:

system catalog only

SQL query:

Click on query to copy it

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,
unnest(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,
unnest(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_grouped as (
select fk.conname, fk.foreign_schema, foreign_table, array_agg(fk.foreign_table || '.' || a_foreign.attname order by  a_foreign.attnum) as foreign_col, 
fk.target_schema, fk.target_table, array_agg(fk.target_table  || '.' || a_target.attname  order by  a_target.attnum) as target_col,
array_agg(a_target.attnotnull order by  a_target.attnum) as target_not_null
from fk inner join pg_attribute a_foreign on fk.foreign_col = 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 = a_target.attnum and fk.target_table_oid = a_target.attrelid and a_target.attisdropped = false
group by fk.conname, fk.foreign_schema, fk.foreign_table,  fk.target_schema, fk.target_table)
select conname, foreign_schema as schema, foreign_table as table, foreign_col, target_col
from fk_grouped
where foreign_schema=target_schema 
and foreign_table=target_table 
and not(target_not_null @> array['f']::boolean[])
and (not(foreign_table~*'(user|person|client|customer|isik|subjekt|kasutaja|klient)') or target_col::text!~*'(_by|create|modif|delete|creator|looja|muutja|registreerija|kustutaja)')
order by foreign_schema, foreign_table;

SQL statements for generating SQL statements that help us to fix the problem

SQL query	Description
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, unnest(o.confkey) AS foreign_col, (select nspname from pg_namespace where oid=m.relnamespace) as target_schema, m.relname as target_table, m.oid as target_table_oid, unnest(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 inner join pg_class m on m.oid = o.conrelid where o.contype = 'f' and o.conrelid in (select oid from pg_class c where c.relkind = 'r')), fk_grouped as ( select fk.conname, fk.foreign_schema, foreign_table, fk.target_schema, fk.target_table, array_agg(a_target.attname order by a_target.attnum) as target_col, array_agg(a_target.attnotnull order by a_target.attnum) as target_not_null from fk inner join pg_attribute a_foreign on fk.foreign_col = 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 = a_target.attnum and fk.target_table_oid = a_target.attrelid and a_target.attisdropped = false group by fk.conname, fk.foreign_schema, fk.foreign_table, fk.target_schema, fk.target_table) select format('ALTER TABLE %1$I.%2$I ALTER COLUMN %3$I DROP NOT NULL;', foreign_schema, foreign_table, unnest(target_col)) AS statements from fk_grouped where foreign_schema=target_schema and foreign_table=target_table and not(target_not_null @> array['f']::boolean[]) order by foreign_schema, foreign_table;	Drop the NOT NULL constraint that is associated directly with the table, i.e., not through a domain.

SQL query

Description

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,
unnest(o.confkey) AS foreign_col,
(select nspname from pg_namespace where oid=m.relnamespace) as target_schema,
m.relname as target_table, 
m.oid as target_table_oid,
unnest(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 
inner join pg_class m on m.oid = o.conrelid
where o.contype = 'f' and o.conrelid in (select oid from pg_class c where c.relkind = 'r')),
fk_grouped as (
select fk.conname, fk.foreign_schema, foreign_table, 
fk.target_schema, fk.target_table, array_agg(a_target.attname  order by  a_target.attnum) as target_col,
array_agg(a_target.attnotnull order by  a_target.attnum) as target_not_null
from fk inner join pg_attribute a_foreign on fk.foreign_col = 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 = a_target.attnum and fk.target_table_oid = a_target.attrelid and a_target.attisdropped = false
group by fk.conname, fk.foreign_schema, fk.foreign_table,  fk.target_schema, fk.target_table)
select format('ALTER TABLE %1$I.%2$I ALTER COLUMN %3$I DROP NOT NULL;', foreign_schema, foreign_table, unnest(target_col)) AS statements
from fk_grouped
where foreign_schema=target_schema and foreign_table=target_table and not(target_not_null @> array['f']::boolean[])
order by foreign_schema, foreign_table;

Drop the NOT NULL constraint that is associated directly with the table, i.e., not through a domain.

Collections where the query belongs to

Collection name	Collection description
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 .

Collection name

Collection description

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 .

Categories where the query belongs to

Category name	Category description
Hierarchical data	Queries of this catergory provide information about storing hierarchical data in the database.
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.
Result quality depends on names	Queries of this category use names (for instance, column names) to try to guess the meaning of a database object. Thus, the goodness of names determines the number of false positive and false negative results.

Category name

Category description

Hierarchical data

Queries of this catergory provide information about storing hierarchical data in the database.

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.

Result quality depends on names

Queries of this category use names (for instance, column names) to try to guess the meaning of a database object. Thus, the goodness of names determines the number of false positive and false negative results.