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
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.
Type
Problem detection (Each row in the result could represent a flaw in the design)
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
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, '; ' 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,''), '; ' 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 that help generate fixes for the identified problem.
SQL Query to Generate Fix
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
This query belongs to the following collections:
Name
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
This query is classified under the following categories:
Name
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.