Goal This query identifies multiple-column CHECK constraints that explicitly check for NULL values. In general, constraint definitions should be kept as simple as possible. Because a NULL value causes a logical condition to evaluate to UNKNOWN—and CHECK constraints inherently allow rows that evaluate to either TRUE or UNKNOWN—there is usually no need to explicitly allow missing values. For instance, instead of writing CHECK (last_update_time IS NULL OR last_update_time >= creation_time), the constraint should simply be written as CHECK (last_update_time >= creation_time). However, a valid exception exists for implication rules (P ⇒ Q), which can be rewritten as NOT (P) OR Q. For example, the constraint CHECK (NOT (product IS NOT NULL) OR service IS NULL) properly enforces the rule that if a product is present, the service must be NULL. Such logical constructs are entirely appropriate.
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)
Data Source INFORMATION_SCHEMA+system catalog
SQL Query 
WITH expressions AS (select 
n.nspname as schema,
c.relname || '.' || o.conname as name, 
substring(pg_get_constraintdef(o.oid),7) as expression,
'TABLE CHECK' AS type
from pg_constraint o inner join pg_class c on c.oid = o.conrelid
inner join pg_namespace n on n.oid=c.relnamespace
where o.contype ='c' and cardinality(o.conkey)>1
and n.nspname not in (select schema_name
from information_schema.schemata
where schema_name<>'public' and
schema_owner='postgres' and schema_name is not null))
SELECT schema, name, expression, type
FROM expressions
WHERE
   expression ~* '(\y[a-zA-Z_][a-zA-Z0-9_]*\y)\W+IS\s+NULL\y.*\yOR\y.*\y\1\y'
   OR 
   expression ~* '(\y[a-zA-Z_][a-zA-Z0-9_]*\y)\y.*\yOR\y.*\y\1\W+IS\s+NULL\y'
ORDER BY schema, type, 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.

Missing data

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

NameDescription
CHECK constraintsQueries of this category provide information about CHECK constraints.
Missing dataQueries of this category provide information about missing data (NULLs) in a database.