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The following page has been changed by RaghothamMurthy: http://wiki.apache.org/hadoop/Hive/LanguageManual/LanguageManual/Union ------------------------------------------------------------------------------ + - Syntax: - {{{ - select_statement UNION ALL select_statement UNION ALL select_statement ... - }}} - UNION is used to combine the result from multiple SELECT statements into a single result set. We currently only support UNION ALL (bag union) i.e. duplicates are not eliminated. The number and names of columns returned by each select_statement has to be the same. Otherwise, a schema error is thrown. - - If some additional processing has to be done on the result of the UNION, the entire statement expression can be embedded in a FROM clause like below: - {{{ - SELECT * - FROM ( - select_statement - UNION ALL - select_statement - ) unionResult - }}} - - - For example, if we suppose there are two different tables that track which user has published a video and which user has published a comment, the following query joins the results of a union all with the user table to create a single annotated stream for all the video publishing and comment publishing events: - {{{ - SELECT u.id, actions.date - FROM ( - SELECT av.uid AS uid - FROM action_video av - WHERE av.date = '2008-06-03' - UNION ALL - SELECT ac.uid AS uid - FROM action_comment ac - WHERE ac.date = '2008-06-03' - ) actions JOIN users u ON (u.id = actions.uid) - }}} -
