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  2. Join (SQL) - Wikipedia

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

    Some database systems allow the user to force the system to read the tables in a join in a particular order. This is used when the join optimizer chooses to read the tables in an inefficient order. For example, in MySQL the command STRAIGHT_JOIN reads the tables in exactly the order listed in the query. [16]

  3. Set operations (SQL) - Wikipedia

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

    UNION can be useful in data warehouse applications where tables are not perfectly normalized. [2] A simple example would be a database having tables sales2005 and sales2006 that have identical structures but are separated because of performance considerations. A UNION query could combine results from both tables.

  4. Relational algebra - Wikipedia

    en.wikipedia.org/wiki/Relational_algebra

    The right outer join ( ) behaves almost identically to the left outer join, but the roles of the tables are switched. The right outer join of relations R and S is written as R S. [e] The result of the right outer join is the set of all combinations of tuples in R and S that are equal on their common attribute names, in addition to tuples in S ...

  5. Select (SQL) - Wikipedia

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

    The derived table also is referred to as an inline view or a select in from list. In the following example, the SQL statement involves a join from the initial Books table to the derived table "Sales". This derived table captures associated book sales information using the ISBN to join to the Books table.

  6. Sort-merge join - Wikipedia

    en.wikipedia.org/wiki/Sort-merge_join

    The sort-merge join (also known as merge join) is a join algorithm and is used in the implementation of a relational database management system. The basic problem of a join algorithm is to find, for each distinct value of the join attribute, the set of tuples in each relation which display that value. The key idea of the sort-merge algorithm is ...

  7. Query by Example - Wikipedia

    en.wikipedia.org/wiki/Query_by_Example

    Query by Example (QBE) is a database query language for relational databases. 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.

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  9. Merge (SQL) - Wikipedia

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

    A right join is employed over the Target (the INTO table) and the Source (the USING table / view / sub-query)--where Target is the left table and Source is the right one. The four possible combinations yield these rules: