executor: distinct error

[fzhedu]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. What did you do?

diff --git a/sessionctx/variable/tidb_vars.go b/sessionctx/variable/tidb_vars.go

-       DefInitChunkSize                   = 32
-       DefMaxChunkSize                    = 1024
+       DefInitChunkSize                   = 2
+       DefMaxChunkSize                    = 2

diff --git a/sessionctx/variable/varsutil.go b/sessionctx/variable/varsutil.go
-       maxChunkSizeLowerBound = 32
+       maxChunkSizeLowerBound = 1

download the file with all DDLs
randgen_index_merge_join.txt

source randgen_index_merge_join.txt
set @@tidb_max_chunk_size=2;

SELECT DISTINCT  table2 . `col_int_key` AS field1 FROM  P AS table1  RIGHT  JOIN P AS table2 ON  table1 . `pk` =  table2 . `pk`  WHERE table2 . `pk` <= table2 . `col_int`   ORDER BY field1  LIMIT 100 ;

2. What did you expect to see?

+--------+
| field1 |
+--------+
|   NULL |
|      0 |
|      2 |
|      4 |
|      8 |
+--------+

3. What did you see instead?

mysql> SELECT DISTINCT  table2 . `col_int_key` AS field1 FROM  P AS table1  RIGHT  JOIN P AS table2 ON  table1 . `pk` =  table2 . `pk`  WHERE table2 . `pk` <= table2 . `col_int`   ORDER BY field1  LIMIT 100 ;
+--------+
| field1 |
+--------+
|   NULL |
|      2 |
|      4 |
|      8 |
+--------+
4 rows in set (0.00 sec)

mysql> explain SELECT DISTINCT  table2 . `col_int_key` AS field1 FROM  P AS table1  RIGHT  JOIN P AS table2 ON  table1 . `pk` =  table2 . `pk`  WHERE table2 . `pk` <= table2 . `col_int`   ORDER BY field1  LIMIT 100 ;
+-----------------------------------+---------+-----------+----------------------------------------------+-------------------------------------------------------------------------------------------------------------------------------------------------+
| id                                | estRows | task      | access object                                | operator info                                                                                                                                   |
+-----------------------------------+---------+-----------+----------------------------------------------+-------------------------------------------------------------------------------------------------------------------------------------------------+
| Limit_15                          | 5.76    | root      |                                              | offset:0, count:100                                                                                                                             |
| └─StreamAgg_33                    | 5.76    | root      |                                              | group by:randgen_index_merge_join.p.col_int_key, funcs:firstrow(randgen_index_merge_join.p.col_int_key)->randgen_index_merge_join.p.col_int_key |
|   └─IndexLookUp_37                | 7.20    | root      |                                              |                                                                                                                                                 |
|     ├─IndexFullScan_34(Build)     | 9.00    | cop[tikv] | table:table2, index:col_int_key(col_int_key) | keep order:true, stats:pseudo                                                                                                                   |
|     └─Selection_36(Probe)         | 7.20    | cop[tikv] |                                              | le(randgen_index_merge_join.p.pk, randgen_index_merge_join.p.col_int)                                                                           |
|       └─TableRowIDScan_35         | 9.00    | cop[tikv] | table:table2                                 | keep order:false, stats:pseudo                                                                                                                  |
+-----------------------------------+---------+-----------+----------------------------------------------+-------------------------------------------------------------------------------------------------------------------------------------------------+
6 rows in set (0.01 sec)

mysql> 

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

5.7.25-TiDB-v4.0.0-beta-523-g7eba696bb

[XuHuaiyu]

minor case:

create table t(a int);
insert into t values(null),(null);
insert into t values(0),(2),(2),(4),(8);
select /*+ stream_agg() */ distinct * from t;