Null (SQL)
In SQL, 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 fulfil 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.
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- enThe Codd table Emp may represent the relation EmpH22 or EmpH37, as pictured.
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- enIn SQL, 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 fulfil 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.
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- enclass="wikitable" style="display: inline-table !important" + Emp ! Name !! Age George 43 Harriet Charles 56 class="wikitable" style="display: inline-table !important" + EmpH22 ! Name !! Age George 43 Harriet 22 Charles 56 class="wikitable" style="display: inline-table !important" + EmpH37 ! Name !! Age George 43 Harriet 37 Charles 56
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- 12 April 2013
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- enIn SQL, 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 fulfil 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. A null should not be confused with a value of 0. A null value indicates a lack of a value, which is not the same thing as a value of zero. For example, consider the question "How many books does Adam own?" The answer may be "zero" (we know that he owns none) or "null" (we do not know how many he owns). 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 Adam owns no books. SQL null is a marker, not a value. This usage is quite different from most programming languages, where null value of a reference means it is not pointing to any object.
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- zenodo.org/record/1038419%7Cdoi=10.3233/978-1-60750-690-4-354%7Cyear=2011
- archive.org/details/databaserelation00date
- www.thethirdmanifesto.com/
- www.iaeng.org/IJCS/issues_v35/issue_3/IJCS_35_3_08.pdf
- www.psoug.org/reference/null.html
- web.archive.org/web/20130412031441/http:/psoug.org/reference/null.html
- www09.sigmod.org/sigmod/record/issues/0809/p23.grant.pdf
- ceur-ws.org/Vol-866/paper8.pdf
- www.u.arizona.edu/~rubinson/scrawl/Rubinson.2007.Nulls_Three-Valued_Logic_and_Ambiguity_in_SQL.pdf
- www.acm.org/sigmod/record/issues/9409/sql.ps
- web.archive.org/web/20130405060544/http:/www.sqlexpert.co.uk/2006/05/treatment-of-nulls-by-oracle-sql.html
- bugs.sun.com/bugdatabase/view_bug.do%3Fbug_id=4032732
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- Null (SQL)
- Null (SQL)
- Null (SQL)
- Null (SQL)
- Null (SQL)
- Null (SQL)
- Null (SQL)
- NULL (SQL)
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