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Null (SQL)

In the SQL database query language, .mw-parser-output .monospaced{font-family:monospace,monospace}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…

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Overview

History

Null propagation

Comparisons with NULL and the three-valued logic (3VL)

Analysis of SQL Null missing-value semantics

Check constraints and foreign keys

Outer joins

Aggregate functions

Effect on index operation

Null-handling functions

Data typing of Null and Unknown

BOOLEAN data type

Controversy

Advanced semantic analysis

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Map overview Semantic statistics

Null (SQL)

Nodes107
Edges106
Triples0
Avg. degree1.98
Density0.018692
Components1

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Important terminology Word statistics

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Important terminology

sql null nulls value unknown example database logic data codd query missing rows result following information would standard one however

Entity relationships Subject–Predicate–Object triples

SubjectPredicateObjectConfidenceSrc

Related concept clusters Concept neighborhoods

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    Connections between topic areas Semantic bridges

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