Details
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New Feature
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Status: Open
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Major
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Resolution: Unresolved
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Description
mysql calls them hidden columns/indeterminate results. See:
http://dev.mysql.com/doc/refman/5.0/en/group-by-hidden-columns.html
they are immensely useful. Many a time, i am joining a dimension table on it's unique key with a fact table and then a group to compute aggregates over fact table columns. i want to get a row with some/all the columns of the dimension table along with aggregates on columns in the fact table. Very standard use case.
In this case, one is forced to do a group by on not just the unique (join) key - but all the columns from the dimension table required in the final result. This is unnecessarily wasteful. We only need to group by on the unique key and then emit dimension table columns from one of the rows per group.