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- Consider the possibility of multiple map-joins on different keys:
Code Block select /*+MAPJOIN(smallTableTwo)*/ idOne, idTwo, value FROM ( select /*+MAPJOIN(smallTableOne)*/ idOne, idTwo, value FROM bigTable JOIN smallTableOne on (bigTable.idOne = smallTableOne.idOne) ) firstjoin JOIN smallTableTwo on (firstjoin.idTwo = smallTableTwo.idTwo)
The above query is not supported. Without the mapjoin hint, the above query would be executed as 2 map-only jobs. If the user knows in advance that the inputs are small enough to fit in memory, the following configurable parameters can be used to make sure that the query executes in a single map-reduce job.
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