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• Null_(SQL) abstract "Null is a special marker used in Structured Query Language (SQL) 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. NULL is also an SQL reserved keyword used to identify the Null special marker.For people new to the subject, a good way to remember what null means is to remember that in terms of information, \"lack of a value\" is not the same thing as \"a value of zero\"; similarly, \"lack of an answer\" is not the same thing as \"an answer of no\". For example, consider the question \"How many books does Juan own?\" The answer may be \"zero\" (we know that he owns none) or \"null\" (we do not know how many he owns, or doesn't own). In a database table, the column reporting this answer would start out with no value (marked by Null), and it would not be updated with the value \"zero\" until we have ascertained that Juan owns no books.SQL null is a state (unknown) and not a value. This usage is quite different from most programming languages, where null means not assigned to a particular instance.".
• Null_(SQL) thumbnail Db_null.png?width=300.
• Null_(SQL) wikiPageExternalLink www.thethirdmanifesto.com.
• Null_(SQL) wikiPageExternalLink view_bug.do?bug_id=4032732.
• Null_(SQL) wikiPageExternalLink paper8.pdf.
• Null_(SQL) wikiPageExternalLink sql.ps.
• Null_(SQL) wikiPageExternalLink IJCS_35_3_08.pdf.
• Null_(SQL) wikiPageExternalLink null.html.
• Null_(SQL) wikiPageExternalLink treatment-of-nulls-by-oracle-sql.html.
• Null_(SQL) wikiPageExternalLink the-nature-of-null.
• Null_(SQL) wikiPageExternalLink Rubinson.2007.Nulls_Three-Valued_Logic_and_Ambiguity_in_SQL.pdf.
• Null_(SQL) wikiPageExternalLink p23.grant.pdf.
• Null_(SQL) wikiPageID "2002540".
• Null_(SQL) wikiPageLength "58057".
• Null_(SQL) wikiPageOutDegree "108".
• Null_(SQL) wikiPageRevisionID "698309391".
• Null_(SQL) wikiPageWikiLink ACM_Transactions_on_Database_Systems.
• Null_(SQL) wikiPageWikiLink Aggregate_function.
• Null_(SQL) wikiPageWikiLink Association_for_Computing_Machinery.
• Null_(SQL) wikiPageWikiLink B-tree.
• Null_(SQL) wikiPageWikiLink NULLs_and_the_Three_Valued_Logic.
• Null_(SQL) wikiPageWikiLink Boolean_data_type.
• Null_(SQL) wikiPageWikiLink Category:Articles_with_example_SQL_code.
• Null_(SQL) wikiPageWikiLink Category:SQL_keywords.
• Null_(SQL) wikiPageWikiLink Category:Unknown_content.
• Null_(SQL) wikiPageWikiLink Check_constraint.
• Null_(SQL) wikiPageWikiLink Christopher_J._Date.
• Null_(SQL) wikiPageWikiLink Closed-world_assumption.
• Null_(SQL) wikiPageWikiLink Co-NP-complete.
• Null_(SQL) wikiPageWikiLink Codds_12_rules.
• Null_(SQL) wikiPageWikiLink Computerworld.
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• Null_(SQL) wikiPageWikiLink Conditional_(computer_programming).
• Null_(SQL) wikiPageWikiLink Conditional_table.
• Null_(SQL) wikiPageWikiLink Constant_function.
• Null_(SQL) wikiPageWikiLink D_(data_language_specification).
• Null_(SQL) wikiPageWikiLink Data_definition_language.
• Null_(SQL) wikiPageWikiLink Data_domain.
• Null_(SQL) wikiPageWikiLink Data_manipulation_language.
• Null_(SQL) wikiPageWikiLink Data_type.
• Null_(SQL) wikiPageWikiLink Database_theory.
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• Null_(SQL) wikiPageWikiLink Donald_D._Chamberlin.
• Null_(SQL) wikiPageWikiLink Edgar_F._Codd.
• Null_(SQL) wikiPageWikiLink Fabian_Pascal.
• Null_(SQL) wikiPageWikiLink False_dilemma.
• Null_(SQL) wikiPageWikiLink File:Sql_query1.png.
• Null_(SQL) wikiPageWikiLink Foreign_key.
• Null_(SQL) wikiPageWikiLink Function_overloading.
• Null_(SQL) wikiPageWikiLink Functional_completeness.
• Null_(SQL) wikiPageWikiLink Greek_alphabet.
• Null_(SQL) wikiPageWikiLink Hugh_Darwen.
• Null_(SQL) wikiPageWikiLink IBM_System_R.
• Null_(SQL) wikiPageWikiLink Information.
• Null_(SQL) wikiPageWikiLink International_Association_of_Engineers.
• Null_(SQL) wikiPageWikiLink Is_functions.
• Null_(SQL) wikiPageWikiLink Join_(SQL).
• Null_(SQL) wikiPageWikiLink Law_of_excluded_middle.
• Null_(SQL) wikiPageWikiLink Literal_(computer_programming).
• Null_(SQL) wikiPageWikiLink Microsoft_SQL_Server.
• Null_(SQL) wikiPageWikiLink MySQL.
• Null_(SQL) wikiPageWikiLink Omega.
• Null_(SQL) wikiPageWikiLink Open-world_assumption.
• Null_(SQL) wikiPageWikiLink SQL.
• Null_(SQL) wikiPageWikiLink Pearson_PLC.
• Null_(SQL) wikiPageWikiLink Possible_world.
• Null_(SQL) wikiPageWikiLink PostgreSQL.
• Null_(SQL) wikiPageWikiLink Procedural_programming.
• Null_(SQL) wikiPageWikiLink Propositional_calculus.
• Null_(SQL) wikiPageWikiLink Tasmania.
• Null_(SQL) wikiPageWikiLink Relational_algebra.
• Null_(SQL) wikiPageWikiLink Relational_database_management_system.
• Null_(SQL) wikiPageWikiLink Relational_model.
• Null_(SQL) wikiPageWikiLink Reserved_word.
• Null_(SQL) wikiPageWikiLink Reverse_Polish_notation.
• Null_(SQL) wikiPageWikiLink SIGMOD.
• Null_(SQL) wikiPageWikiLink SQL.
• Null_(SQL) wikiPageWikiLink SQL-92.
• Null_(SQL) wikiPageWikiLink PSM.
• Null_(SQL) wikiPageWikiLink SQL:1999.
• Null_(SQL) wikiPageWikiLink SQL:2003.
• Null_(SQL) wikiPageWikiLink SQL_Server_Compact.
• Null_(SQL) wikiPageWikiLink SQLite.
• Null_(SQL) wikiPageWikiLink Semipredicate_problem.
• Null_(SQL) wikiPageWikiLink Skolem_normal_form.
• Null_(SQL) wikiPageWikiLink Structure_(mathematical_logic).
• Null_(SQL) wikiPageWikiLink Switch_statement.
• Null_(SQL) wikiPageWikiLink Tautology_(logic).
• Null_(SQL) wikiPageWikiLink Telephone_number.
• Null_(SQL) wikiPageWikiLink The_Third_Manifesto.
• Null_(SQL) wikiPageWikiLink Three-valued_logic.
• Null_(SQL) wikiPageWikiLink Transact-SQL.
• Null_(SQL) wikiPageWikiLink Undefined_value.
• Null_(SQL) wikiPageWikiLink File:Db_null.png.
• Null_(SQL) wikiPageWikiLinkText "".
• Null_(SQL) wikiPageWikiLinkText "NOT NULL".
• Null_(SQL) wikiPageWikiLinkText "NULL".
• Null_(SQL) wikiPageWikiLinkText "NULLs are to be avoided".
• Null_(SQL) wikiPageWikiLinkText "NULLs".
• Null_(SQL) wikiPageWikiLinkText "Null (SQL)".

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