This query identifies superfluous CHECK constraints by detecting logical subsumption. It targets columns where a generic validation ensuring the trimmed string is not empty (e.g., trim(column) <> '') is rendered redundant by a more specific constraint that enforces a minimum length on the trimmed string (e.g., char_length(trim(column)) > 0). Since a string with a positive length is inherently not empty, the generic check adds no functional value and should be removed to simplify the schema.
Type
Problem detection (Each row in the result could represent a flaw in the design)
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, '; ') 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~*'length\(trim\([^\)]+\)\)[[:space:]]*>(=){0,1}[[:space:]]*[[:digit:]]')
AND
(constraints~*'trim\([^\)]+\)[[:space:]]*<>[[:space:]]*''''')
ORDER BY table_schema, table_name, column_name;
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.
Duplication of implementation elements
Queries of this catergory provide information about the duplication of the database objects.