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The "Hive/LanguageManual/Joins" page has been changed by NamitJain. http://wiki.apache.org/hadoop/Hive/LanguageManual/Joins?action=diff&rev1=13&rev2=14 -------------------------------------------------- SELECT a.key, a.val FROM a LEFT SEMI JOIN b on (a.key = b.key) }}} + * If all but one of the tables being joined are small, the join can be performed as a map only job. The query + {{{ + SELECT /*+ MAPJOIN(b) */ a.key, a.value + FROM a join b on a.key = b.key + }}} + does not need a reducer. For every mapper of A, B is read completely. The restriction is that '''a FULL/RIGHT OUTER JOIN b''' cannot be performed * If the tables being joined are bucketized, and the buckets are a multiple of each other, the buckets can be joined with each other. If table A has 8 buckets are table B has 4 buckets, the following join {{{ SELECT /*+ MAPJOIN(b) */ a.key, a.value
