Sergei Petrunia 9b4dfdaa5a MDEV-13352: Server crashes in st_join_table::remove_duplicates ...

join_tab->distinct=true means "Before doing record read with this
join_tab, call join_tab->remove_duplicates() to eliminate duplicates".
remove_duplicates() assumes that
- there is a temporary table $T with rows that are to be de-duplicated
- there is a previous join_tab (e.g. with join_tab->fields) which was
used to populate the temp.table $T.

When the query has "Impossible WHERE" and window function, then the above
conditions are not met (but we still might need a window function
computation step when the query has implicit grouping).

The fix is to not add remove_duplicates step if the select execution is
degenerate (and we'll have at most one row in the output anyway).

2018-01-22 13:44:31 +03:00

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