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MSDN documentation on UNION in Transact-SQL for SQL Server; Naming of select list items in set operations; UNION in MySQL with Examples; UNION in MySQL; UNION Clause in PostgreSQL; SQL UNION and UNION ALL; Sort order within UNION statement; Designing a data flow that loads a warehouse table; Oracle 11g documentation for UNION (ALL), INTERSECT ...
Nested Sets is a clever solution – maybe too clever. It also fails to support referential integrity. It’s best used when you need to query a tree more frequently than you need to modify the tree. [9] The model doesn't allow for multiple parent categories. For example, an 'Oak' could be a child of 'Tree-Type', but also 'Wood-Type'.
The resulting forest contains a single tree whose root is n, and the path from 1 to n passes through every node in the tree. For this forest, the time to run Find(1) is O(n). In an efficient implementation, tree height is controlled using union by size or union by rank. Both of these require a node to store information besides just its parent ...
The relational algebra uses set union, set difference, and Cartesian product from set theory, and adds additional constraints to these operators to create new ones.. For set union and set difference, the two relations involved must be union-compatible—that is, the two relations must have the same set of attributes.
PostgreSQL includes built-in support for regular B-tree and hash table indexes, and four index access methods: generalized search trees , generalized inverted indexes (GIN), Space-Partitioned GiST (SP-GiST) [42] and Block Range Indexes (BRIN). In addition, user-defined index methods can be created, although this is quite an involved process.
For example, PostgreSQL versions 8.1 and later implement a "bitmap index scan" optimization to speed up arbitrarily complex logical operations between available indexes on a single table. For tables with many columns, the total number of distinct indexes to satisfy all possible queries (with equality filtering conditions on either of the fields ...
This is a tagged union with two cases: one, the leaf, is used to terminate a path of the tree, and functions much like a null value would in imperative languages ...
A disjoint union of an indexed family of sets (:) is a set , often denoted by , with an injection of each into , such that the images of these injections form a partition of (that is, each element of belongs to exactly one of these images). A disjoint union of a family of pairwise disjoint sets is their union.