Find check constraints of base table and foreign table columns that are either associated with more than one column and have at least one AND operation or are associated with exactly one column and have two or more AND operations.
Notes
The query finds CHECK constraints that are associated with a base table directly as well as CHECK constraints that are associated with domains that are used to define at least one column. The query does not find CHECK constraints of domains that are not associated with any table. The query may give false positive results if the constraint uses BETWEEN … AND … predicate. The query excludes constraints where subconditions are connected by the OR operator because in this case a rule could be that if a condition P holds a condition Q must also hold. For instance, if in the column X is value 'A' and in the column Y is value 'B', then in the column Z there must be value 'C'. The query excludes constraints with the Boolean expression NOT (P AND Q) where P and Q are subconditions on different columns.
Type
Problem detection (Each row in the result could represent a flaw in the design)
Increase separation of concerns in case of CHECK constraints by creating multiple smaller check constraints instead of one big constraint. Instead of one CHECK constraint with multiple sub-conditions create multiple CHECK constraints.
Data Source
INFORMATION_SCHEMA only
SQL Query
WITH checks AS (SELECT ccu.table_schema, ccu.table_name, t.table_type, ccu.column_name, cc.check_clause, cc.constraint_name, 'TABLE CHECK' AS check_type, NULL AS domain_schema, NULL AS domain_name
FROM INFORMATION_SCHEMA.constraint_column_usage AS ccu INNER JOIN INFORMATION_SCHEMA.check_constraints AS cc USING (constraint_schema, constraint_name)
INNER JOIN INFORMATION_SCHEMA.tables AS t USING (table_schema, table_name)
WHERE cc.check_clause NOT LIKE '%IS NOT NULL' AND
ccu.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)
UNION SELECT cdu.table_schema, cdu.table_name, t.table_type, cdu.column_name, cc.check_clause, cc.constraint_name, 'DOMAIN CHECK' AS check_type, cdu.domain_schema, cdu.domain_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.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)),
checks_columns AS (SELECT table_schema, table_name, table_type, array_agg(column_name) AS columns, check_clause, constraint_name, check_type, domain_schema, domain_name
FROM checks
GROUP BY table_schema, table_name, table_type, check_clause, constraint_name, check_type, domain_schema, domain_name)
SELECT table_schema, table_name, table_type, columns, check_clause, check_clause, constraint_name, check_type, domain_schema, domain_name
FROM checks_columns
WHERE check_clause!~*'[[:space:]]OR[[:space:]]'
AND (
(check_type='TABLE CHECK' AND cardinality(columns)>1
AND check_clause~*'((.*[[:space:]]AND[[:space:]].*){2,}|(?
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.
Comfortability of database evolution
Queries of this category provide information about the means that influence database evolution.
Further reading and related materials:
Reference
The corresponding code smell in case of cleaning code is "G30: Functions Should Do One Thing". (Robert C. Martin, Clean Code)