Lesson plan

Expression index

Within computing and computer science, an expression index, also known as a function based index, is a database index that is built on a generic expression, rather than one or more columns. This allows indexes to be defined for common query conditions that depend on data in a table, but are not actually stored in that table. A common use for an expression index is to support case-insensitive searching or constraints. For example, if a web site wants to make user names case-insensitive, but still preserve the case as originally entered by the user, an index can be created on the lower-case representation of the user name: : CREATE INDEX users__last_name_lower ON users( lower( last_name ) ); That will create a unique index on "lower(last_name)". Any queries that search on "lower(last_name)" could then make use of that index: : SELECT user_id FROM users WHERE lower( last_name ) = lower( 'Smith' );

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Article summary

Within computing and computer science, an expression index, also known as a function based index, is a database index that is built on a generic expression, rather than one or more columns. This allows indexes to be defined for common query conditions that depend on data in a table, but are not actually stored in that table. A common use for an expression index is to support case-insensitive searching or constraints. For example, if a web site wants to make user names case-insensitive, but still preserve the case as originally entered by the user, an index can be created on the lower-case representation of the user name: : CREATE INDEX users__last_name_lower ON users( lower( last_name ) ); That will create a unique index on "lower(last_name)". Any queries that search on "lower(last_name)" could then make use of that index: : SELECT user_id FROM users WHERE lower( last_name ) = lower( 'Smith' );

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  1. Summarise the article in your own words. Which single claim would you verify first, and why?
  2. Which claim in this article is most likely to be revised as the sources update? How would you check its current status?
  3. If two sources disagreed about one of these facts, what would you need in order to trust one over the other?

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