Join Hints
Updated: March 10, 2017
In addition to the JOIN operators, U-SQL optionally allows the query author to provide hints on the type of join to choose and what parallel join execution to use.
| Syntax |
|---|
Join_Hints :=
[Parallel_Join_Hint] [Join_Algorithm_Hint]. |
These hints impact the plan generation of the query optimizer. If the optimizer cannot find a succession of optimizer rules to satisfy the requested hints, for example because the hints are not applicable to a specific JOIN, a NO PLAN error will be raised.
These hints are best used with care, since specifying a certain hint will make it impossible for the optimizer to find a better plan. They should only be used if the default plan is not optimal.
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