IS NULL check is probably not needed

Query goal:

Find CHECK constraints that refer only to mandatory columns but the Boolean expression has IS NULL condition.

Notes about the query:

The query considers CHECK constraints that are associated with a column directly as well as through a domain. The query considers check constraints that involve multiple columns.

Query type:

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

Query reliability:

High (Few or no false-positive results)

Query license:

MIT License

Fixing suggestion:

Drop the check constraint if it is not needed.

Data source:

INFORMATION_SCHEMA only

SQL query:

Click on query to copy it

WITH table_checks AS (SELECT ccu.table_schema, ccu.table_name, ccu.column_name, cc.check_clause, cc.constraint_name
FROM INFORMATION_SCHEMA.constraint_column_usage AS ccu INNER JOIN INFORMATION_SCHEMA.check_constraints AS cc
USING (constraint_schema, constraint_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, cdu.column_name, cc.check_clause, cc.constraint_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_catalog, constraint_schema, constraint_name)
WHERE t.table_type='BASE TABLE' 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 catalog_name IS NOT NULL AND schema_name IS NOT NULL)) 
SELECT  table_schema, table_name, check_clause, constraint_name
FROM table_checks INNER JOIN information_schema.columns USING (table_schema, table_name, column_name)
WHERE check_clause~*'IS[[:space:]]*NULL'
GROUP BY table_schema, table_name,  check_clause, constraint_name
HAVING Count(*) FILTER (WHERE is_nullable='NO')=Count(*)
ORDER BY table_schema, table_name, constraint_name;

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

SQL query	Description
WITH table_checks AS (SELECT ccu.table_schema, ccu.table_name, ccu.column_name, cc.check_clause, cc.constraint_name FROM INFORMATION_SCHEMA.constraint_column_usage AS ccu INNER JOIN INFORMATION_SCHEMA.check_constraints AS cc USING (constraint_schema, constraint_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)) SELECT format('ALTER TABLE %1$I.%2$I DROP CONSTRAINT %3$I;', table_schema, table_name, constraint_name) AS statements FROM table_checks INNER JOIN information_schema.columns USING (table_schema, table_name, column_name) WHERE check_clause~'IS[[:space:]]NULL' GROUP BY table_schema, table_name, check_clause, constraint_name HAVING Count() FILTER (WHERE is_nullable='NO')=Count() ORDER BY table_schema, table_name, constraint_name;	Drop the constraint of the base table

SQL query

Description

WITH table_checks AS (SELECT ccu.table_schema, ccu.table_name, ccu.column_name, cc.check_clause, cc.constraint_name
FROM INFORMATION_SCHEMA.constraint_column_usage AS ccu INNER JOIN INFORMATION_SCHEMA.check_constraints AS cc
USING (constraint_schema, constraint_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)) 
SELECT format('ALTER TABLE %1$I.%2$I DROP CONSTRAINT %3$I;', table_schema, table_name, constraint_name) AS statements
FROM table_checks INNER JOIN information_schema.columns USING (table_schema, table_name, column_name)
WHERE check_clause~*'IS[[:space:]]*NULL'
GROUP BY table_schema, table_name,  check_clause, constraint_name
HAVING Count(*) FILTER (WHERE is_nullable='NO')=Count(*)
ORDER BY table_schema, table_name, constraint_name;

Drop the constraint of the base table

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.
Missing data	Queries of this category provide information about missing data (NULLs) in a database.
Validity and completeness	Queries of this category provide information about whether database design represents the world (domain) correctly (validity) and whether database design captures all the information about the world (domain) that is correct and relevant (completeness).

Category name

Category description

CHECK constraints

Queries of this category provide information about CHECK constraints.

Missing data

Queries of this category provide information about missing data (NULLs) in a database.

Validity and completeness

Queries of this category provide information about whether database design represents the world (domain) correctly (validity) and whether database design captures all the information about the world (domain) that is correct and relevant (completeness).