Page History

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• Vectorization will be turned off for delete operations.  This is automatic and requires no action on the part of the user.  Non-delete operations are not affected.  Tables with deleted data can still be queried using vectorization.
• In version 0.14 it is recommended that you set hive.optimize.sort.dynamic.partition=false when doing deletes, as this produces more efficient execution plans.

Merge

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Standard Syntax:
MERGE INTO <target table> AS T USING <source expression/table> AS S
ON <boolean expression1>
WHEN MATCHED [AND <boolean expression2>] THEN UPDATE SET <set clause list>
WHEN MATCHED [AND <boolean expression3>] THEN DELETE
WHEN NOT MATCHED [AND <boolean expression4>] THEN INSERT VALUES<value list>

Synopsis

• Merge allows actions to be performed on a target table based on the results of a join with a source table.
• In Hive 2.2, upon successful completion of this operation the changes will be auto-committed.

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SQL Standard requires that an error is raised if the ON clause is such that more than 1 row in source matches a row in target.  This check is computationally expensive and may affect the overall runtime of a MERGE statement significantly.  hive.merge.cardinality.check=false may be used to disable the check at your own risk.  If the check is disabled, but the statement has such a cross join effect, it may lead to data corruption.

Notes

• 1, 2, or 3 WHEN clauses may be present; at most 1 of each type: UPDATE UPDATE/DELETE/INSERT.
• WHEN NOT MATCHED must be the last WHEN clause.
• If both UPDATE and DELETE clauses are present, the 1st first one in the statement must include [AND <boolean expression>].
• Vectorization will be turned off for merge operations.  This is automatic and requires no action on the part of the user.  Non-delete operations are not affected.  Tables with deleted data can still be queried using vectorization.

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