bug: explain `estimated rows` is zero when select * from stage

[BohuTANG]

Summary

Count:

mysql> select count() from @lake (pattern => '.*parquet');
+----------+
| count()  |
+----------+
| 10000000 |
+----------+

explain:

mysql> explain select * from @lake (pattern => '.*parquet');
+--------------------------------------------------+
| explain                                          |
+--------------------------------------------------+
| TableScan                                        |
| ├── table: default.system.read_parquet           |
| ├── read rows: 10000000                          |
| ├── read bytes: 1552567904                       |
| ├── partitions total: 9766                       |
| ├── partitions scanned: 9766                     |
| ├── push downs: [filters: [], limit: NONE]       |
| └── estimated rows: 0.00                         |
+--------------------------------------------------+

[BohuTANG]

cc @leiysky @xudong963

[leiysky]

The cause is that the StageTable doesn't implement Table::table_statistics.

@dantengsky Is it possible to generate table statistics for stage tables?

[BohuTANG]

@youngsofun is working on it(stage) :)

[youngsofun]

for parquet，we can get num rows after read partition