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Some query tools can generate embedded hints in the query, for use by the optimizer. Some databases - like Oracle - provide a plan table for query tuning. This plan table will return the cost and time for executing a query. Oracle offers two optimization approaches: CBO or Cost Based Optimization; RBO or Rule Based Optimization
The goal of optimization is therefore either to find the best query plan based on some specification of user preferences provided as input to the optimizer (e.g., users can define weights between different cost metrics to express relative importance or define hard cost bounds on certain metrics) or to generate an approximation of the set of ...
A common table expression, or CTE, (in SQL) is a temporary named result set, derived from a simple query and defined within the execution scope of a SELECT, INSERT, UPDATE, or DELETE statement. CTEs can be thought of as alternatives to derived tables ( subquery ), views , and inline user-defined functions.
The SQL SELECT statement returns a result set of rows, from one or more tables. [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.
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 ...
TIME: for time values (e.g. 15:51:36). 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.
StreamSQL extends the type system of SQL to support streams in addition to tables. Several new operations are introduced to manipulate streams. Selecting from a stream - A standard SELECT statement can be issued against a stream to calculate functions (using the target list) or filter out unwanted tuples (using a WHERE clause). The result will ...
It uses a sequence-based hi-lo pattern to generate values. Hi/Lo is used in scenarios where an application needs its entities to have an identity prior to persistence. It is a value generation strategy. An alternative to Hi/Lo would be for the application to generate keys as universally unique identifiers (UUID).