July 2010
Intermediate to advanced
840 pages
16h 33m
English
Content preview from Joe Celko's SQL for Smarties, 3rd Edition
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Chapter 25. Arrays in SQL
ARRAYS CANNOT BE REPRESENTED directly in SQL-92, but they are a common vendor language extension that became part of SQL-99. Arrays violate the rules of First Normal Form (1NF) required for a relational database, which say that the tables have no repeating groups in any column. A repeating group is a data structure that is not scalar; examples of repeating groups include linked lists, arrays, records, and even tables within a column.
The reason they are not allowed is that a repeating group would have to define a column like a data type. There is no obvious way to JOIN a column that contains an array to other columns, since there are no comparison operators or conversion rules. There is no obvious way to display or ...
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