Adjust the estimated row count when push Limit and keep order for partitioned table #40986
Description
Enhancement
When there's a Limit above a scan operator, we should adjust the estimated row count of the scan operator accordingly.
But when we push Limit and keep order for a partitioned table (introduced in #36108 as a temporary enhancement), we didn't do this:
use test;
create table t (a int, b int, c int, index ia(a)) partition by range(b) (partition p1 values less than(100), partition p2 values less than(200), partition p3 values less than maxvalue);
analyze table t;
explain select a from t where a > 10 order by a limit 10;+-----------------------------+---------+-----------+----------------------+-------------------------------------------------+
| id | estRows | task | access object | operator info |
+-----------------------------+---------+-----------+----------------------+-------------------------------------------------+
| TopN_8 | 10.00 | root | | test.t.a, offset:0, count:10 |
| └─IndexReader_15 | 10.00 | root | partition:all | index:Limit_14 |
| └─Limit_14 | 10.00 | cop[tikv] | | offset:0, count:10 |
| └─IndexRangeScan_13 | 3333.33 | cop[tikv] | table:t, index:ia(a) | range:(10,+inf], keep order:false, stats:pseudo |
+-----------------------------+---------+-----------+----------------------+-------------------------------------------------+
Normally, if it's not a partitioned table, the estimated row count is like this:
use test;
create table t1 (a int, b int, c int, index ia(a));
analyze table t1;
explain select a from t1 order by a limit 10;+----------------------------+---------+-----------+-----------------------+-------------------------------+
| id | estRows | task | access object | operator info |
+----------------------------+---------+-----------+-----------------------+-------------------------------+
| Limit_10 | 10.00 | root | | offset:0, count:10 |
| └─IndexReader_18 | 10.00 | root | | index:Limit_17 |
| └─Limit_17 | 10.00 | cop[tikv] | | offset:0, count:10 |
| └─IndexFullScan_16 | 10.00 | cop[tikv] | table:t1, index:ia(a) | keep order:true, stats:pseudo |
+----------------------------+---------+-----------+-----------------------+-------------------------------+