![]() ![]() RDBMS products that support common table expressions: The rest of the queries follow the standard formats for simple and complex SQL SELECT queries. In the syntax documentation above, the occurrence of alias_name is a meaningful name you would give to the sub-query after the AS clause. AS(sql_subquery_statement_from_alias_name_A When using multiple sub-queries syntax can be as below ![]() The following is the syntax of the SQL WITH clause when using a single subquery alias. This is derived from a simple query and defined within the execution scope of a single SELECT, INSERT, UPDATE, or DELETE statement. It specifies a temporary named result set, known as a common table expression (CTE). The WITH clause is also known as common table expression (CTE) and subquery factoring. Database optimizes the query by treating the query name as either an inline view or as a temporary table You can then reference the subquery block multiple places in the query by specifying the query name. The WITH query_name clause lets you assign a name to a subquery block. This makes it possible to improve the structure of a statement without polluting the global namespace. ![]() They are not stored in the database schema: instead, they are only valid in the query they belong to. To make it better, in 1999 SQL added WITH clause to define “statement scoped views”. In 1992, to make queries reusable SQL introduced views. So once we create a view, it has a name in the database schema so that other queries can use it like a table. ![]()
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