Everything About ___
Live briefing

Everything about Null (SQL)

Marker used in SQL databases to indicate a value does not exist

In the SQL database query language, null or NULL is a special marker used to indicate that a data value does not exist in the database. Introduced by the creator of the relational database model, E. F. Codd, SQL null serves to fulfill the requirement that all true relational database management systems (RDBMS) support a representation of "missing information and inapplicable information". Codd also introduced the use of the lowercase Greek omega (ω) symbol to represent null in database theory. In SQL, NULL is a reserved word used to identify this marker. Wikipedia →

🧭 Start here: a 6-step reading path

  1. Read the overview: Null (SQL)A 5-minute orientation
  2. Pick up a classic book: Database system conceptsThe most-reprinted book on the subject
  3. Read the landmark paper: Null values in SQLCited 11 times
  4. Go sideways: SQL syntaxA closely related topic
  5. Go sideways: SQLA closely related topic

📖 Definitions

No dictionary entry for this exact phrase.

🗂️ The subject at a glance

  1. History
  2. Null propagation
  3. Comparisons with NULL and the three-valued logic (3VL)
  4. Analysis of SQL Null missing-value semantics
  5. Check constraints and foreign keys
  6. Outer joins
  7. Aggregate functions
  8. When two nulls are equal: grouping, sorting, and some set operations
  9. Effect on index operation
  10. Null-handling functions
  11. Data typing of Null and Unknown
  12. BOOLEAN data type

🏆 Landmark papers (most cited)

📚 Books worth reading

Ranked by number of editions on Open Library, a rough measure of how lasting a book is.

🔗 Related topics