Goal This query identifies superfluous CHECK constraints by detecting logical subsumption. It targets columns where a general non-blankness constraint is made redundant by a more specific, format-validating constraint. For instance, if an e_mail column is validated by a format constraint from Set1 (e.g., e_mail LIKE '%@%'), that constraint implicitly ensures the string is not blank. Therefore, any co-existing constraint from Set2 (e.g., e_mail !~ '^[[:space:]]*$') is logically unnecessary and can be removed to reduce schema complexity.

Example. Set1: {e_mail~'[[:alnum:]@]+'; position('@' in e_mail)>0; e_mail LIKE '%@%'} Set2: {e_mail~'\S'; e_mail!~'^[[:space:]]*$'; e_mail!~'^\s*$'} If column e_mail has a constraint from Set1, then it does not need a constraint from Set2.
Notes The query gives false positive results if permitted symbols include whitespace characters. Thus, "Mrs Smith" is permitted but a string that consist of only spaces is not permitted.
Type Problem detection Each row in the result could represent a flaw in the design
Reliability Medium Medium number of false-positive results
License MIT (opens in new tab)
Fixing Suggestion Remove redundant constraints that are covered by other constraints.
Data Source INFORMATION_SCHEMA+system catalog
SQL Query 
WITH checks AS (
select 
n.nspname as table_schema,
c.relname as table_name,
CASE WHEN c.relkind='r' THEN 'BASE TABLE' ELSE 'FOREIGN' END AS table_type,
a.attname as column_name,
regexp_replace(pg_get_constraintdef(o.oid),'CHECK ', '','g') AS check_clause,
'TABLE CHECK' AS check_type, 
o.conname AS constraint_name
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
AND c.relkind IN ('r', 'f')
UNION ALL SELECT cdu.table_schema, cdu.table_name, t.table_type, cdu.column_name, regexp_replace(cc.check_clause, 'VALUE', '(' || cdu.column_name ||')::' || lower(d.data_type)) AS check_clause, 'DOMAIN CHECK' AS check_type, 
d.domain_schema||'.'||d.domain_name || '.' || cc.constraint_name AS name
FROM INFORMATION_SCHEMA.column_domain_usage AS cdu INNER JOIN INFORMATION_SCHEMA.tables AS t USING (table_schema, table_name) 
INNER JOIN INFORMATION_SCHEMA.domain_constraints AS dc USING (domain_schema, domain_name) 
INNER JOIN INFORMATION_SCHEMA.domains AS d USING (domain_schema, domain_name)
INNER JOIN INFORMATION_SCHEMA.check_constraints AS cc USING (constraint_schema, constraint_name)
WHERE t.table_type IN ('BASE TABLE', 'FOREIGN') AND cc.check_clause NOT LIKE '%IS NOT NULL'  AND 
cdu.table_schema NOT IN (SELECT schema_name
FROM INFORMATION_SCHEMA.schemata
WHERE schema_name<>'public' AND
schema_owner='postgres' AND schema_name IS NOT NULL)),
aggregate_checks AS (SELECT table_schema, table_name, column_name, string_agg (check_clause, ';<br>') AS constraints
FROM checks
GROUP BY table_schema, table_name, column_name)
SELECT table_schema, table_name, column_name, constraints
FROM aggregate_checks
WHERE ((constraints~'[[:space:]]~[*]{0,1}[[:space:]]+[^~]*([+]|[{][123456789])'
OR constraints~*'(position[[:space:]]*\(.+>|<.+position[[:space:]]*\()'
OR constraints~*'(length[[:space:]]*\([[:space:]]*trim[[:space:]]*\(.+>[[:space:]]*0|0[[:space:]]*<.+length[[:space:]]*\([[:space:]]*trim[[:space:]]*\()'
OR constraints~'[[:space:]]~~[[:space:]]'
OR (constraints~'[[:space:]]~[*]{0,1}[[:space:]]+''[\^]{0,1}[^\^ '']+[\$]{0,1}'''
AND constraints!~*'(space|\\s|\.\*)')) AND constraints!~'[[:space:]]~[*]{0,1}[[:space:]]+''[^'']* [^'']*''')
AND 
(constraints~'[[:space:]]<>[[:space:]]+''[ ]*'''
OR constraints~'[[:space:]]!~[*]{0,1}[[:space:]]+''[\^][[]{2}[:]space[:][]]{2}[*+]{0,1}[$]'''
OR constraints~'[[:space:]]!~[*]{0,1}[[:space:]]+''[\^]\\s[*+]{0,1}[$]'
OR constraints~'[[:space:]]~[*]{0,1}[[:space:]]+''\\S'''
OR constraints~'[[:space:]]~[*]{0,1}[[:space:]]+''\[\^\[\:space\:\]\]''')
ORDER BY table_schema, table_name, column_name;

Collections

This query belongs to the following collections:

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 .

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:

CHECK constraints

Queries of this category provide information about CHECK constraints.

Duplication of implementation elements

Queries of this catergory provide information about the duplication of the database objects.

NameDescription
CHECK constraintsQueries of this category provide information about CHECK constraints.
Duplication of implementation elementsQueries of this catergory provide information about the duplication of the database objects.