Not-null constraint
A NOT NULL constraint is a database rule requiring every row in a column to contain a value other than SQL NULL.
Learn SQL in a Month of Lunches
A NOT NULL constraint is a database rule that requires a column to contain a non-null value in every row.
- How it is used
- Enforces required values while designing shipment and author-payment tables.
- How deep it goes
- Defines nullable columns, walks through column-by-column decisions, and contrasts NOT NULL with DEFAULT and CHECK constraints.
- Examples
- Uses shipment records, optional author middle names, and required author-payment identifiers and years.
- What you can do after
- Build it from scratch by marking required CREATE TABLE columns NOT NULL and preserving nullable optional fields.
Read how Learn SQL in a Month of Lunches explains not-null constraint →
Java Persistence with Spring Data and Hibernate epub
A NOT NULL constraint is a database rule requiring a column to contain a value rather than SQL NULL.
- How it is used
- Protects required database values while exposing nullability tradeoffs in ORM inheritance mappings.
- How deep it goes
- Explains schema declarations, Hibernate behavior, inheritance limitations, secondary tables, and strategy tradeoffs.
- Examples
- Uses BillingDetails owner mapping and CreditCard fields moved into a CREDITCARD secondary table.
- What you can do after
- Evaluate inheritance mappings and configure explicit database nullability for required entity properties.
Read how Java Persistence with Spring Data and Hibernate epub explains not-null constraint →
Just Use Postgres!
A NOT NULL constraint requires a column value to be present rather than SQL NULL.
- How it is used
- Enforces required column values at the database level while creating or modifying application tables.
- How deep it goes
- Defines the rule, shows column declarations and ALTER TABLE usage, and stops short of internal constraint mechanics.
- Examples
- Uses product catalog name and description columns, customer review text, and psql schema output.
- What you can do after
- Operate/configure PostgreSQL tables by declaring required columns and adding NOT NULL constraints with psql and SQL.
Grokking Relational Database Design
A NOT NULL constraint requires a column to contain a non-NULL value.
- How it is used
- Uses NOT NULL to protect required data during table design and implementation.
- How deep it goes
- Defines the constraint, explains NULL-related problems, and demonstrates column syntax without covering database-engine internals.
- Examples
- Demonstrates product columns, user-account fields, legal data, and foreign-key relationships as candidates for NOT NULL.
- What you can do after
- Apply NOT NULL by identifying required attributes and declaring the constraint in CREATE TABLE statements.
Read how Grokking Relational Database Design explains not-null constraint →
Rust Servers, Services, and Apps
A NOT NULL constraint requires every row in a database column to contain a non-null value.
- How it is used
- Enforces required course fields at the database boundary while the Rust data model evolves.
- How deep it goes
- Defines required columns in SQL and aligns them with non-optional Rust fields, without detailing constraint internals.
- Examples
- Uses tutor_id and course_name in the ezy_course_c6 SQL table, with psql commands for execution and inspection.
- What you can do after
- Operate/configure a SQL schema with required columns and verify it through psql.
Read how Rust Servers, Services, and Apps explains not-null constraint →
Build Financial Software with Generative AI (From Scratch)
A NOT NULL constraint requires a database column to contain a value rather than SQL NULL.
- How it is used
- Enforces required values in relational database columns, supporting reliable ACH exception and file records.
- How deep it goes
- Defines the constraint and applies it in schemas, but does not descend into database engine internals.
- Examples
- Uses ACH file identifiers, record numbers, exception codes, and nullable record-type references in database table definitions.
- What you can do after
- Operate/configure database schemas by marking fields that every stored row must populate.
Read how Build Financial Software with Generative AI (From Scratch) explains not-null constraint →
Related concepts
- constraintkind of · A constraint is a condition or rule that restricts the permissible states, values, actions, or solutions in a system or problem.
- data integrityproduces · Data integrity is the property that data remains accurate, complete, consistent, and valid, with changes made only through authorized actions.
- missing valuecontrasts with · A missing value is a marker or condition indicating that an expected data value or reference is absent, unavailable, unknown, or inapplicable.
- default valuecontrasts with · A default value is a predefined or automatically supplied value used when an expected input, argument, field, or configuration setting is omitted or unspecified.
- primary keyconfigured by · A primary key is a designated column or attribute, or combination of them, that uniquely identifies each row or item in a table or data store.
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