[MDEV-11096] Wrong number of filtered rows for a table in EXPLAIN EXTENDED Created: 2016-10-21  Updated: 2016-11-15  Resolved: 2016-11-15

Status: Closed
Project: MariaDB Server
Component/s: Optimizer
Affects Version/s: 10.0.27
Fix Version/s: 10.0.29

Type: Bug Priority: Minor
Reporter: Igor Babaev Assignee: Igor Babaev
Resolution: Fixed Votes: 0
Labels: None


 Description   

EXPLAIN EXTENDED always returns 0.00 percentage of filtered rows if there is a range condition over the column for which no statistics has been collected:

The following test case demonstrates the problem:

set use_stat_tables='preferably';
set optimizer_use_condition_selectivity=3;
 
create table t1(col1 char(32));
insert into t1 values ('a'),('b'),('c'),('d'), ('e'),('f'),('g'),('h');
analyze table t1 persistent for columns () indexes ();
explain extended 
select * from t1 where col1 > 'b' and col1 < 'd';
 
MariaDB [test]> explain extended 
    -> select * from t1 where col1 > 'b' and col1 < 'e';
+------+-------------+-------+------+---------------+------+---------+------+------+----------+-------------+
| id   | select_type | table | type | possible_keys | key  | key_len | ref  | rows | filtered | Extra       |
+------+-------------+-------+------+---------------+------+---------+------+------+----------+-------------+
|    1 | SIMPLE      | t1    | ALL  | NULL          | NULL | NULL    | NULL |    8 |     0.00 | Using where |
+------+-------------+-------+------+---------------+------+---------+------+------+----------+-------------+



 Comments   
Comment by Igor Babaev [ 2016-11-15 ]

The fix for this bug was pushed into the 10.0.tree

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