6.481 USER_JOINGROUPS
USER_JOINGROUPS describes join groups belonging to the user. A join group is a user-created object that consists of two or more columns that can be meaningfully joined. The maximum number of columns that can be included in a join group is 255. The USER_JOINGROUPS columns (except for JOINGROUP_OWNER) are the same as those in DBA_JOINGROUPS.
In certain queries, join groups enable the database to eliminate the performance overhead of decompressing and hashing column values. Join groups require an In-Memory column store (IM column store).
See Also:
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Oracle Database In-Memory Guide for an introduction to join groups
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Oracle Database SQL Language Reference for information about creating a join group using the
CREATE INMEMORY JOIN GROUPstatement