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SQL

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SQL is a Structured Query Language used to describe queries that retreive data from relational databases. SAS implements SQL through the SQL procedure.

Concepts

See Beginner to Intermediate uses of SQL for more details.

SQL implements 8 fundamental relational data manipulation concepts, five of which are commonly encountered:

  • SELECTION - Select only certain rows meeting certain criteria
  • PROJECTION – Select only certain columns
  • UNION – Take all rows belonging to any of several tables
  • INTERSECTION – Take all rows belonging to all of several tables
  • (DIFFERENCE) – Take all rows belonging to only one of several tables
  • JOIN - Join columns of tables by linking on rows describing common entities
  • (PRODUCT) - Join columns of tables but without linking on rows describing common entities
  • AGGREGATION – Numerically summarize – e.g. average– rows with common elements
  • (DIVISION)– Summarize rows with common elements in a different table

History

For more information see Structured Query Language#History

SQL was first described in 1974 in a paper, published by IBM, titled SEQUEL: A Structured Query Language. This paper included an appendix describing the syntax of SEQUEL. However, IBM's use of the acronym SEQUEL was subsequently challenged as a claim was made that SEQUEL was a trademark of the Hawker Siddeley Aircraft Company in Great Britain. Rather than challenge the claim, the authors chose to drop the vowels from the acronym, thus arriving at SQL.

Standards

SQL is an international standard that is sometimes implemented by various manufacturers in slightly different ways to the common standard.

Implementations

Further reading