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).

1 files changed, 10 insertions, 0 deletions

diff --git a/mysql-test/t/win.test b/mysql-test/t/win.test
index 1e747e59a1a..95ffb6d9909 100644
--- a/mysql-test/t/win.test
+++ b/mysql-test/t/win.test
@@ -2057,3 +2057,13 @@ SELECT id, window
 FROM door as window;
 
 DROP TABLE door;
+
+--echo #
+--echo # MDEV-13352: Server crashes in st_join_table::remove_duplicates
+--echo #
+CREATE TABLE t1 (i INT);
+INSERT INTO t1 VALUES (1),(2);
+SELECT DISTINCT ROW_NUMBER() OVER(), i FROM t1 WHERE 0;
+SELECT ROW_NUMBER() OVER(), i FROM t1 WHERE 0;
+DROP TABLE t1;
+