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The joined table retains each row—even if no other matching row exists. Outer joins subdivide further into left outer joins, right outer joins, and full outer joins, depending on which table's rows are retained: left, right, or both (in this case left and right refer to the two sides of the JOIN keyword).
The outer join ( ) or full outer join in effect combines the results of the left and right outer joins. The full outer join is written as R S where R and S are relations. [f] The result of the full 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 that have ...
New set operations such as UNION, UNION ALL, CROSS JOIN, and formalized JOIN types (INNER JOIN, LEFT JOIN, RIGHT JOIN, FULL OUTER JOIN). Conditional expressions with CASE. For an example, see Case (SQL). Support for alterations of schema definitions via ALTER and DROP. Bindings for C, Ada, and MUMPS. New features for user privileges.
Queries can be nested so that the results of one query can be used in another query via a relational operator or aggregation function. A nested query is also known as a subquery. While joins and other table operations provide computationally superior (i.e. faster) alternatives in many cases, the use of subqueries introduces a hierarchy in ...
Right outer and Full outer joins are pretty rare but have come up. Use UNION of queries many many times. Inner Joins are NOT always faster than Left outer joins. Any complex query has many other considerations than just slamming in inner joins everywhere.
In response to a query, the database returns a result set. Often, data from multiple tables are combined into one, by doing a join. Conceptually, this is done by taking all possible combinations of rows (the Cartesian product), and then filtering out everything except the answer. There are a number of relational operations in addition to 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 ...
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: