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  2. Database index - Wikipedia

    en.wikipedia.org/wiki/Database_index

    A database index is a data structure that improves the speed of data retrieval operations on a database table at the cost of additional writes and storage space to maintain the index data structure. Indexes are used to quickly locate data without having to search every row in a database table every time said table is accessed.

  3. Comparison of online source code playgrounds - Wikipedia

    en.wikipedia.org/wiki/Comparison_of_online...

    Db2, Firebird, MariaDB, MySQL, Node.js, Oracle, Postgres, SQL Server, SQLite, YugabyteDB ExtendsClass [an] Free Yes No No Yes MySQL, SQLite (SQL.js) PhpFiddle [ao] Free Yes No No Yes MySQL, SQLite runnable [aj] Free Yes Yes Yes No SQL Fiddle [ap] Free No No No Yes MySQL, Oracle, PostgreSQL, SQLite (WebSQL), SQLite (SQL.js) W3Schools [ae] Free ...

  4. Query by Example - Wikipedia

    en.wikipedia.org/wiki/Query_by_Example

    It was devised by Moshé M. Zloof at IBM Research during the mid-1970s, in parallel to the development of SQL. [1] It is the first graphical query language, using visual tables where the user would enter commands, example elements and conditions. Many graphical front-ends for databases use the ideas from QBE today.

  5. W3Schools - Wikipedia

    en.wikipedia.org/wiki/W3Schools

    W3Schools is a freemium educational website for learning coding online. [1] [2] Initially released in 1998, it derives its name from the World Wide Web but is not affiliated with the W3 Consortium. [3] [4] [unreliable source] W3Schools offers courses covering many aspects of web development. [5] W3Schools also publishes free HTML templates.

  6. Wikipedia:Request a query/Tips and schemas - Wikipedia

    en.wikipedia.org/wiki/Wikipedia:Request_a_query/...

    Most tables have many indexes, but you need to use the correct combination and order of fields in order to benefit from them. Avoid the revision table, because it literally has a billion rows If you only need to check recent page revisions (last 30 days), use the recentchanges table instead of the revision table. If you can get the data you ...

  7. Join (SQL) - Wikipedia

    en.wikipedia.org/wiki/Join_(SQL)

    The Oracle implementation limits itself to using bitmap indexes. A bitmap join index is used for low-cardinality columns (i.e., columns containing fewer than 300 distinct values, according to the Oracle documentation): it combines low-cardinality columns from multiple related tables. The example Oracle uses is that of an inventory system, where ...

  8. Select (SQL) - Wikipedia

    en.wikipedia.org/wiki/Select_(SQL)

    Title Authors ----- ----- SQL Examples and Guide 4 The Joy of SQL 1 An Introduction to SQL 2 Pitfalls of SQL 1 Under the precondition that isbn is the only common column name of the two tables and that a column named title only exists in the Book table, one could re-write the query above in the following form:

  9. Correlated subquery - Wikipedia

    en.wikipedia.org/wiki/Correlated_subquery

    In a SQL database query, a correlated subquery (also known as a synchronized subquery) is a subquery (a query nested inside another query) that uses values from the outer query. This can have major impact on performance because the correlated subquery might get recomputed every time for each row of the outer query is processed.