planner: use ExtraHandleColumn as PK when generating TablePath

[francis0407]

What problem does this PR solve?

Before this PR:

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

mysql> explain select * from t where a > 10 order by _tidb_rowid;
+-------------------------+----------+------+------------------------------------------------------------+
| id                      | count    | task | operator info                                              |
+-------------------------+----------+------+------------------------------------------------------------+
| Projection_6            | 3333.33  | root | test.t.a, test.t.b                                         |
| └─Sort_7                | 3333.33  | root | test.t._tidb_rowid:asc                                     |
|   └─TableReader_11      | 3333.33  | root | data:Selection_10                                          |
|     └─Selection_10      | 3333.33  | cop  | gt(test.t.a, 10)                                           |
|       └─TableScan_9     | 10000.00 | cop  | table:t, range:[-inf,+inf], keep order:false, stats:pseudo |
+-------------------------+----------+------+------------------------------------------------------------+
5 rows in set (0.00 sec)

After this PR:

mysql> explain select * from t where a > 10 order by _tidb_rowid;
+------------------------+-------+------+-----------------------------------------------------------+
| id                     | count | task | operator info                                             |
+------------------------+-------+------+-----------------------------------------------------------+
| Projection_6           | 1.33  | root | test.t.a, test.t.b                                        |
| └─TableReader_14       | 1.33  | root | data:Selection_13                                         |
|   └─Selection_13       | 1.33  | cop  | gt(test.t.a, 10)                                          |
|     └─TableScan_12     | 4.00  | cop  | table:t, range:[-inf,+inf], keep order:true, stats:pseudo |
+------------------------+-------+------+-----------------------------------------------------------+
4 rows in set (0.00 sec)

What is changed and how it works?

This PR makes getPKIsHandleCol() return ExtraHandleColumn instead of nil when the table has no PK.

Check List

Tests

• Unit test

Release note

When the table uses _tidb_rowid as Handle, we can correctly generate a TableScan that can keep the order of _tidb_rowid. For example, select max(_tidb_rowid) from t won't require a Sort anymore.

[codecov]

Codecov Report

Merging #11959 into master will not change coverage.
The diff coverage is n/a.

@@             Coverage Diff             @@
##             master     #11959   +/-   ##
===========================================
  Coverage   81.2949%   81.2949%           
===========================================
  Files           444        444           
  Lines         95092      95092           
===========================================
  Hits          77305      77305           
  Misses        12305      12305           
  Partials       5482       5482

[zz-jason]

@francis0407 Please add proper labels.

[alivxxx]

LGTM

[zz-jason]

LGTM

[sre-bot]

/run-all-tests

[sre-bot]

@francis0407 merge failed.

[winoros]

/build

[francis0407]

/run-cherry-picker

[sre-bot]

cherry pick to release-2.1 failed

[sre-bot]

cherry pick to release-3.0 failed

[sre-bot]

cherry pick to release-3.1 failed