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The number 0, the strings "0" and "", the empty list (), and the special value undef evaluate to false. [8] All else evaluates to true. Lua has a Boolean data type, but non-Boolean values can also behave as Booleans. The non-value nil evaluates to false, whereas every other data type value evaluates to true.
This is misleading: the {} is interpreted as an empty code block instead of an empty object, and the empty array is cast to a number by the remaining unary + operator. If the expression is wrapped in parentheses - ({} + []) – the curly brackets are interpreted as an empty object and the result of the expression is "[object Object]" as ...
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.
A simple B+ tree example linking the keys 1–7 to data values d 1-d 7. The linked list (red) allows rapid in-order traversal. This particular tree's branching factor is =4. Both keys in leaf and internal nodes are colored gray here. By definition, each value contained within the B+ tree is a key contained in exactly one leaf node.
The most frequently used general-purpose implementation of an associative array is with a hash table: an array combined with a hash function that separates each key into a separate "bucket" of the array. The basic idea behind a hash table is that accessing an element of an array via its index is a simple, constant-time operation. Therefore, the ...
In computer science, a composite data type or compound data type is a data type that consists of programming language scalar data types and other composite types that may be heterogeneous and hierarchical in nature.
The elements used for a skip list can contain more than one pointer since they can participate in more than one list. Insertions and deletions are implemented much like the corresponding linked-list operations, except that "tall" elements must be inserted into or deleted from more than one linked list.
SQL was initially developed at IBM by Donald D. Chamberlin and Raymond F. Boyce after learning about the relational model from Edgar F. Codd [12] in the early 1970s. [13] This version, initially called SEQUEL (Structured English Query Language), was designed to manipulate and retrieve data stored in IBM's original quasirelational database management system, System R, which a group at IBM San ...