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An ORDER BY clause in SQL specifies that a SQL SELECT statement returns a result set with the rows being sorted by the values of one or more columns. The sort criteria does not have to be included in the result set (restrictions apply for SELECT DISTINCT, GROUP BY, UNION [DISTINCT], EXCEPT [DISTINCT] and INTERSECT [DISTINCT].)
The ORDER BY clause identifies which columns to use to sort the resulting data, and in which direction to sort them (ascending or descending). Without an ORDER BY clause, the order of rows returned by an SQL query is undefined. The DISTINCT keyword [5] eliminates duplicate data. [6] The following example of a SELECT query returns a list of ...
The ORDER BY clause identifies which column[s] to use to sort the resulting data, and in which direction to sort them (ascending or descending). Without an ORDER BY clause, the order of rows returned by an SQL query is undefined. The DISTINCT keyword [3] eliminates duplicate data. [4]
Typically, readers can sort data in ascending or descending order based on the values in the selected column. The first click on the header cell will sort the column’s data in ascending order, a second click of the same arrow descending order, and a third click will restore the original order of the entire table.
compute the columns to keep (SELECT line). (if union-clause present) combine (union, difference, intersect) the result with the result of another select statement. if DISTINCT, throw out redundant entries. (if ORDER present) order the result by the columns (ascending or descending as specified, with precedence as listed).
A hierarchical query is a type of SQL query that handles hierarchical model data. They are special cases of more general recursive fixpoint queries, which compute transitive closures. In standard SQL:1999 hierarchical queries are implemented by way of recursive common table expressions (CTEs).
Indexes can be created using one or more columns of a database table, providing the basis for both rapid random lookups and efficient access of ordered records. An index is a copy of selected columns of data, from a table, that is designed to enable very efficient search.
An index is a persisted ordering of records in a table. Indexes are used for both sequential access to rows in the order defined, and for direct record navigation based on indexed column values. The order defined by an index is described in terms of an array of columns, in precedence order. This array of columns is also called the index key.