Rows_examined can be reset for sub queries

Bug #807198 reported by Eric Bergen on 2011-07-07
6
This bug affects 1 person
Affects Status Importance Assigned to Milestone
MariaDB
New
Undecided
Michael Widenius

Bug Description

Rows_examined in the slow query log can be reset by the outer query when using a sub query. For these two queries the first one sets Rows_examined correctly but the second one has it reset even though the row stats work correctly.

# Time: 110702 9:44:23
# User@Host: [ebergen] @ localhost []
# Thread_id: 1 Schema: test QC_hit: No
# Query_time: 1.396374 Lock_time: 0.000093 Rows_sent: 1 Rows_examined: 677984
# Row_Stats: test:rows_read=677984,rows_changed=0,rows_changed_x_indexes=0;
# Index_Stats: test:rows_read=677984;
SET timestamp=1309625063;
select count(*) from t2;

# Time: 110702 9:44:49
# User@Host: [ebergen] @ localhost []
# Thread_id: 1 Schema: test QC_hit: No
# Query_time: 2.262701 Lock_time: 0.000126 Rows_sent: 1 Rows_examined: 0
# Row_Stats: test:rows_read=677984,rows_changed=0,rows_changed_x_indexes=0;#temp#:rows_read=0,rows_changed=677984,rows_changed_x_indexes=677984;
# Index_Stats: test:rows_read=677984;
SET timestamp=1309625089;
select count(*) from (select 1 from t2) as t;

The table I'm using looks like:
CREATE TABLE `t2` (
  `t` bigint(20) DEFAULT NULL,
  `u` bigint(20) DEFAULT NULL,
  `b` text,
  KEY `t` (`t`)
) ENGINE=InnoDB DEFAULT CHARSET=latin1

Changed in maria:
assignee: nobody → Michael Widenius (monty)
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