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[1] [2] A SELECT statement retrieves zero or more rows from one or more database tables or database views. In most applications, SELECT is the most commonly used data manipulation language (DML) command. As SQL is a declarative programming language, SELECT queries specify a result set, but
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.
In mathematics and logic, the term "uniqueness" refers to the property of being the one and only object satisfying a certain condition. [1] This sort of quantification is known as uniqueness quantification or unique existential quantification, and is often denoted with the symbols "∃!"
[2] [3] Instead, each element is termed an attribute value. An attribute is a name paired with a domain (nowadays more commonly referred to as a type or data type ). An attribute value is an attribute name paired with an element of that attribute's domain, and a tuple is a set of attribute values in which no two distinct elements have the same ...
A block is a grouping of code that is treated collectively. Many block syntaxes can consist of any number of items (statements, expressions or other units of code) – including one or zero.
Cosmos DB offers two types of indexes: range, supporting range and ORDER BY queries; spatial, supporting spatial queries from points, polygons, and line strings encoded in standard GeoJSON fragments; Containers can also enforce unique key constraints to ensure data integrity. [4]
function Find(x) is if x.parent ≠ x then x.parent := Find(x.parent) return x.parent else return x end if end function This implementation makes two passes, one up the tree and one back down. It requires enough scratch memory to store the path from the query node to the root (in the above pseudocode, the path is implicitly represented using ...
At the most basic definition, "a key is a unique identifier", [1] so unique key is a pleonasm. Keys that are within their originating entity are unique within that entity. Keys that migrate to another entity may or may not be unique, depending on the design and how they are used in the other table.