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MDEV-13352: Server crashes in st_join_table::remove_duplicates

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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).
This commit is contained in:
Sergei Petrunia
2018-01-18 15:25:40 +03:00
parent 4f8555f1f6
commit 9b4dfdaa5a
3 changed files with 29 additions and 1 deletions
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10
mysql-test/r/win.result
View File

@ -3289,3 +3289,13 @@ SELECT id, window
FROM door as window;
ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'window' at line 2
DROP TABLE door;
#
# MDEV-13352: Server crashes in st_join_table::remove_duplicates
#
CREATE TABLE t1 (i INT);
INSERT INTO t1 VALUES (1),(2);
SELECT DISTINCT ROW_NUMBER() OVER(), i FROM t1 WHERE 0;
ROW_NUMBER() OVER() i
SELECT ROW_NUMBER() OVER(), i FROM t1 WHERE 0;
ROW_NUMBER() OVER() i
DROP TABLE t1;

10
mysql-test/t/win.test
View File

@ -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;

10
sql/sql_select.cc
View File

@ -2670,7 +2670,15 @@ bool JOIN::make_aggr_tables_info()
curr_tab->having= having;
having->update_used_tables();
}
curr_tab->distinct= true;
/*
We only need DISTINCT operation if the join is not degenerate.
If it is, we must not request DISTINCT processing, because
remove_duplicates() assumes there is a preceding computation step (and
in the degenerate join, there's none)
*/
if (top_join_tab_count)
curr_tab->distinct= true;
having= NULL;
select_distinct= false;
}