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ASF GitHub Bot commented on TRAFODION-2522: ------------------------------------------- Github user liuyu000 commented on a diff in the pull request: https://github.com/apache/incubator-trafodion/pull/1001#discussion_r105354591 --- Diff: docs/sql_reference/src/asciidoc/_chapters/sql_statements.adoc --- @@ -7784,6 +7784,117 @@ SELECT (SELECT a FROM t1) FROM t GROUP BY (SELECT a FROM t1); SELECT a+1 FROM t GROUP BY 1+a; ``` +[[with_clause_syntax]] +=== Syntax Description of WITH clause + +WITH clause, known as Common Table Expressions (CTEs) or subquery factoring clause, was introduced in the SQL-99 standard and has been implemented into Trafodion R2.1. + +For the complex expression which is referenced multiple times within the body of SELECT Statement, WITH clause assigns it an alias which is treated like a temporary table or an inline view that lasts only for the duration of the query and can be referenced various times in the same query. + +By abstracting the complicated parts of the query into simpler, separate and logical blocks, and materializing result set to prevent from recomputing multiple times as the data can be easily acquired from the disk-based intermediate materialized table rather than requeried with each reference, WITH clause has following advantages: --- End diff -- Got, thanks Dave & Hans. :) > Add WITH Clause > --------------- > > Key: TRAFODION-2522 > URL: https://issues.apache.org/jira/browse/TRAFODION-2522 > Project: Apache Trafodion > Issue Type: Documentation > Reporter: Liu Yu > Assignee: Liu Yu > -- This message was sent by Atlassian JIRA (v6.3.15#6346)