range info in explain is inconsistent for full range

[eurekaka]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?

mysql> create table t(a int, b int, index idx_b(b));
Query OK, 0 rows affected (0.01 sec)

mysql> explain select * from t;
+-------------------+----------+------+------------------------------------------------------------+
| id                | count    | task | operator info                                              |
+-------------------+----------+------+------------------------------------------------------------+
| TableReader_5     | 10000.00 | root | data:TableScan_4                                           |
| └─TableScan_4     | 10000.00 | cop  | table:t, range:[-inf,+inf], keep order:false, stats:pseudo |
+-------------------+----------+------+------------------------------------------------------------+
2 rows in set (0.00 sec)

mysql> explain select b from t use index(idx_b);
+-------------------+----------+------+---------------------------------------------------------------------+
| id                | count    | task | operator info                                                       |
+-------------------+----------+------+---------------------------------------------------------------------+
| IndexReader_5     | 10000.00 | root | index:IndexScan_4                                                   |
| └─IndexScan_4     | 10000.00 | cop  | table:t, index:b, range:[NULL,+inf], keep order:false, stats:pseudo |
+-------------------+----------+------+---------------------------------------------------------------------+
2 rows in set (0.00 sec)

2. What did you expect to see?

Range info in both explain should be [Null, +inf]

3. What did you see instead?

Range info for table scan is [-inf, +inf], which is wrong because the table scan is a full range table scan.

4. What version of TiDB are you using (tidb-server -V or run select tidb_version(); on TiDB)?

mysql> select tidb_version();
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tidb_version()                                                                                                                                                                                                                                                                                                                      |
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Release Version: v3.0.0-beta-25-gb3bdc5d79
Git Commit Hash: b3bdc5d797467f2548fb1bcd59092686ad3238f5
Git Branch: master
UTC Build Time: 2019-01-31 03:05:58
GoVersion: go version go1.11.1 darwin/amd64
Race Enabled: false
TiKV Min Version: 2.1.0-alpha.1-ff3dd160846b7d1aed9079c389fc188f7f5ea13e
Check Table Before Drop: false |
+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+

[eurekaka]

This issue is related with #8588, we can fix them together. Another related issue is #8058.

[zz-jason]

Since TiDB 4.0, we use TableFullScan or IndexFullScan to indicate that the query is performing a full range scan, the range representation is not a problem any more:

TiDB(root@127.0.0.1:test) > explain select * from t;
+-----------------------+----------+-----------+-----------------------------------------+
| id                    | estRows  | task      | operator info                           |
+-----------------------+----------+-----------+-----------------------------------------+
| TableReader_5         | 10000.00 | root      | data:TableFullScan_4                    |
| └─TableFullScan_4     | 10000.00 | cop[tikv] | table:t, keep order:false, stats:pseudo |
+-----------------------+----------+-----------+-----------------------------------------+
2 rows in set (0.01 sec)

TiDB(root@127.0.0.1:test) > explain select b from t use index(idx_b);
+-----------------------+----------+-----------+--------------------------------------------------+
| id                    | estRows  | task      | operator info                                    |
+-----------------------+----------+-----------+--------------------------------------------------+
| IndexReader_5         | 10000.00 | root      | index:IndexFullScan_4                            |
| └─IndexFullScan_4     | 10000.00 | cop[tikv] | table:t, index:b, keep order:false, stats:pseudo |
+-----------------------+----------+-----------+--------------------------------------------------+
2 rows in set (0.00 sec)

[zz-jason]

thanks to @LittleFall