plan cache would be broken if empty range DataSource is converted to TableDual

[eurekaka]

Please answer these questions before submitting your issue. Thanks!

1. What did you do?
   If possible, provide a recipe for reproducing the error.

set prepared-plan-cache-enabled=true first in config.toml and start TiDB using this config file.

MySQL [test]> create table t(a int, b int, index a_idx(a));
Query OK, 0 rows affected (0.01 sec)

MySQL [test]> insert into t values(1,1),(2,2),(null,3);
Query OK, 3 rows affected (0.00 sec)

MySQL [test]> select * from t;
+------+------+
| a    | b    |
+------+------+
|    1 |    1 |
|    2 |    2 |
| NULL |    3 |
+------+------+
3 rows in set (0.00 sec)

MySQL [test]> prepare stmt from 'select * from t where ?';
Query OK, 0 rows affected (0.00 sec)

MySQL [test]> execute stmt using @param;
Empty set (0.00 sec)

MySQL [test]> set @param = true;
Query OK, 0 rows affected (0.00 sec)

MySQL [test]> execute stmt using @param;
Empty set (0.00 sec)

2. What did you expect to see?

last execute statement should return all 3 rows of table.

3. What did you see instead?

empty set returned.

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

MySQL [test]> select tidb_version();
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| tidb_version()                                                                                                                                                                                                                                                                                                                    |
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Release Version: v2.1.0-rc.1-18-geec6899
Git Commit Hash: eec68995689d5811f4d52846586e969652ed8ffc
Git Branch: master
UTC Build Time: 2018-09-01 06:53:29
GoVersion: go version go1.11rc1 linux/amd64
Race Enabled: false
TiKV Min Version: 2.1.0-alpha.1-ff3dd160846b7d1aed9079c389fc188f7f5ea13e
Check Table Before Drop: false |
+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)