Unexpected result of MySQL test with Index Merge Join hint

[SunRunAway]

Bug Report

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1. Minimal reproduce step (Required)

run test [issue_20571] err: sql:SELECT /*+ inl_merge_join(t2) */ count(*) from table_400_ascii_ascii_bin_undef_1 t1 left join table_300_latin1_latin1_bin_undef_2 t2 on t1.  = t2.  and t1.  < 9143449222791010176 where t1.  != -322  order by t1.pk, t2.pk;: failed to run query 
"SELECT /*+ inl_merge_join(t2) */ count(*) from table_400_ascii_ascii_bin_undef_1 t1 left join table_300_latin1_latin1_bin_undef_2 t2 on t1.  = t2.  and t1.  < 9143449222791010176 where t1.  != -322  order by t1.pk, t2.pk;" 
 around line 38, 
we need(340):
SELECT /*+ inl_merge_join(t2) */ count(*) from table_400_ascii_ascii_bin_undef_1 t1 left join table_300_latin1_latin1_bin_undef_2 t2 on t1.  = t2.  and t1.  < 9143449222791010176 where t1.  != -322  order by t1.pk, t2.pk;
count(*)
24424

but got(340):
SELECT /*+ inl_merge_join(t2) */ count(*) from table_400_ascii_ascii_bin_undef_1 t1 left join table_300_latin1_latin1_bin_undef_2 t2 on t1.  = t2.  and t1.  < 9143449222791010176 where t1.  != -322  order by t1.pk, t2.pk;
count(*)
31756

2. What did you expect to see? (Required)

3. What did you see instead (Required)

4. What is your TiDB version? (Required)

https://internal.pingcap.net/idc-jenkins/blue/organizations/jenkins/tidb_ghpr_integration_common_test/detail/tidb_ghpr_integration_common_test/24079/pipeline

the newest master with #20935 (comment)

[ti-srebot]

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