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A range query is a common database operation that retrieves all records where some value is between an upper and lower boundary. [1] For example, list all employees with 3 to 5 years' experience. Range queries are unusual because it is not generally known in advance how many entries a range query will return, or if it will return any at all.
Bernard Chazelle used compress range trees to achieve () query time and () space for range counting. [5] Joseph JaJa and others later improved this query time to O ( log n log log n ) {\displaystyle O\left({\dfrac {\log n}{\log \log n}}\right)} for range counting, which matches a lower bound and is thus asymptotically optimal .
Each -majority query is first answered by finding the query block, or the biggest block that is contained in the provided query rectangle in () time. For the obtained query block, the first 9 τ {\displaystyle {\frac {9}{\tau }}} candidates are returned (without being verified) in O ( 1 / τ ) {\displaystyle O(1/\tau )} time, so this process ...
TIME WITH TIME ZONE: the same as TIME, but including details about the time zone in question. TIMESTAMP : This is a DATE and a TIME put together in one variable (e.g. 2011-05-03 15:51:36.123456 ). TIMESTAMP WITH TIME ZONE : the same as TIMESTAMP , but including details about the time zone in question.
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 ...
In SQL:1999 a recursive (CTE) query may appear anywhere a query is allowed. It's possible, for example, to name the result using CREATE [ RECURSIVE ] VIEW . [ 16 ] Using a CTE inside an INSERT INTO , one can populate a table with data generated from a recursive query; random data generation is possible using this technique without using any ...
As SQL is a declarative programming language, SELECT queries specify a result set, but do not specify how to calculate it. The database translates the query into a "query plan" which may vary between executions, database versions and database software.
Query optimization consists in determining from a query the most efficient manner (or manners) to execute it. Query optimization can be formalized as translating a relational calculus expression delivering an answer A into efficient relational algebraic expressions delivering the same answer A.