Foreign key column has a simple check constraint that is attached directly to the table

Query goal:

Find foreign key columns that are covered by a simple check constraint, i.e., the constraint involves only one column. Look only constraints that are directly associated with the table, i.e., are not specified through a domain. Perhaps the constraint should be defined on the referenced candidate key column.

Notes about the query:

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. The query excludes domains because it is appropriate to use the same domain in case of both foreign key and referenced candidate key column.

Query type:

Problem detection (Each row in the result could represent a flaw in the design)

Query reliability:

Medium (Medium number of false-positive results)

Query license:

MIT License

Fixing suggestion:

Drop the check constraint and create it on the referenced candidate key column if it is not already there.

Data source:

system catalog only

SQL query:

Click on query to copy it

WITH simple_check_constraints AS (
select 
n.nspname as table_schema,
c.relname as table_name,
a.attname as column_name,
o.conname,
pg_get_constraintdef(o.oid) AS constraint_def
from pg_constraint o inner join pg_class c on c.oid = o.conrelid
inner join pg_namespace n on o.connamespace=n.oid
INNER JOIN pg_attribute a ON a.attrelid = c.oid AND a.attnum = o.conkey[1] AND a.attisdropped = FALSE
where o.contype = 'c' AND cardinality(o.conkey)=1),

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, a_foreign.attname as foreign_col, target_schema, target_table, a_target.attname 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)

SELECT scc.table_schema, scc.table_name, scc.column_name, string_agg(DISTINCT scc.conname || ' ' || scc.constraint_def, ';<br>' ORDER BY scc.conname || ' ' || scc.constraint_def) AS checks_on_fk, 
f.conname AS fk_constraint_name, f.foreign_schema, f.foreign_table, f.foreign_col,
string_agg(DISTINCT coalesce(sccf.conname,'') || ' ' || coalesce(sccf.constraint_def,''), ';<br>' ORDER BY coalesce(sccf.conname,'') || ' ' || coalesce(sccf.constraint_def,'')) AS checks_on_candidate_key

FROM simple_check_constraints AS scc INNER JOIN fk_with_names AS f
ON f.target_schema=scc.table_schema  
AND f.target_table=scc.table_name
AND f.target_col=scc.column_name
LEFT JOIN simple_check_constraints AS sccf
ON f.foreign_schema=sccf.table_schema  
AND f.foreign_table=sccf.table_name
AND f.foreign_col=sccf.column_name
GROUP BY scc.table_schema, scc.table_name, scc.column_name, f.conname, f.foreign_schema, f.foreign_table, f.foreign_col
ORDER BY scc.table_schema, scc.table_name, scc.column_name;

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

SQL query	Description
WITH simple_check_constraints AS ( select n.nspname as table_schema, c.relname as table_name, a.attname as column_name, o.conname, pg_get_constraintdef(o.oid) AS constraint_def from pg_constraint o inner join pg_class c on c.oid = o.conrelid inner join pg_namespace n on o.connamespace=n.oid INNER JOIN pg_attribute a ON a.attrelid = c.oid AND a.attnum = o.conkey[1] AND a.attisdropped = FALSE where o.contype = 'c' AND cardinality(o.conkey)=1), 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, a_foreign.attname as foreign_col, target_schema, target_table, a_target.attname 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) SELECT format('ALTER TABLE %1$I.%2$I DROP CONSTRAINT %3$I;', scc.table_schema, scc.table_name, scc.conname) AS statements FROM simple_check_constraints AS scc WHERE EXISTS (SELECT * FROM fk_with_names AS f WHERE f.target_schema=scc.table_schema AND f.target_table=scc.table_name AND f.target_col=scc.column_name) ORDER BY scc.table_schema, scc.table_name, scc.conname;	Drop the check constraint.

SQL query

Description

WITH simple_check_constraints AS (
select 
n.nspname as table_schema,
c.relname as table_name,
a.attname as column_name,
o.conname,
pg_get_constraintdef(o.oid) AS constraint_def
from pg_constraint o inner join pg_class c on c.oid = o.conrelid
inner join pg_namespace n on o.connamespace=n.oid
INNER JOIN pg_attribute a ON a.attrelid = c.oid AND a.attnum = o.conkey[1] AND a.attisdropped = FALSE
where o.contype = 'c' AND cardinality(o.conkey)=1),

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, a_foreign.attname as foreign_col, target_schema, target_table, a_target.attname 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)

SELECT format('ALTER TABLE %1$I.%2$I DROP CONSTRAINT %3$I;', scc.table_schema, scc.table_name, scc.conname) AS statements
FROM simple_check_constraints AS scc 
WHERE EXISTS (SELECT *
FROM fk_with_names AS f
WHERE f.target_schema=scc.table_schema  
AND f.target_table=scc.table_name
AND f.target_col=scc.column_name)
ORDER BY scc.table_schema, scc.table_name, scc.conname;

Drop the check constraint.

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
CHECK constraints	Queries of this category provide information about CHECK constraints.
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.

Category name

Category description

CHECK constraints

Queries of this category provide information about CHECK constraints.

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.