Search results
Results from the WOW.Com Content Network
Typically, grouping is used to apply some sort of aggregate function for each group. [1] [2] The result of a query using a GROUP BY statement contains one row for each group. This implies constraints on the columns that can appear in the associated SELECT clause. As a general rule, the SELECT clause may only contain columns with a unique value ...
The SQL function EXTRACT can be used for extracting a single field (seconds, for instance) of a datetime or interval value. The current system date / time of the database server can be called by using functions like CURRENT_DATE , CURRENT_TIMESTAMP , LOCALTIME , or LOCALTIMESTAMP .
SQL-92 was the third revision of the SQL database query language. Unlike SQL-89, it was a major revision of the standard. Aside from a few minor incompatibilities, the SQL-89 standard is forward-compatible with SQL-92. The standard specification itself grew about five times compared to SQL-89.
A common data warehouse example involves sales as the measure, with customer and product as dimensions. In each sale a customer buys a product. The data can be sliced by removing all customers except for a group under study, and then diced by grouping by product. A dimensional data element is similar to a categorical variable in statistics.
In communications messages, a date-time group (DTG) is a set of characters, usually in a prescribed format, used to express the year, the month, the day of the month, the hour of the day, the minute of the hour, and the time zone, if different from Coordinated Universal Time (UTC).
SQL includes operators and functions for calculating values on stored values. SQL allows the use of expressions in the select list to project data, as in the following example, which returns a list of books that cost more than 100.00 with an additional sales_tax column containing a sales tax figure calculated at 6% of the price.
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 ...
It supports complex analytics query operators, such as calculated columns, searching and filtering on rows, group by-aggregates and joins. [ 25 ] The engine service exposes a relational data model : At the top level ( cluster ) there is a collection of databases, each database contains a collection of tables and stored functions.