Unexpected behavior for case when {false condition} then {subquery...} else {...} end

[solotzg]

Bug Report

Please answer these questions before submitting your issue. Thanks!

ref #34217

1. Minimal reproduce step (Required)

DROP TABLE IF EXISTS t1;
DROP TABLE IF EXISTS t2;
create table t1(c1 int);
insert into t1 values(2), (3);

select * from t1 where (case when 0 <> 0 then (select c1 from t1) else 0 end) > 1; 
explain select * from t1 where (case when 0 <> 0 then (select c1 from t1) else 0 end) > 1; 
select * from t1 where (case when (select count(1) from t1) = 0 then (select c1 from t1) else 0 end) > 1; 

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

MySQL

mysql> select * from t1 where (case when 0 <> 0 then (select c1 from t1) else 0 end) > 1; 
Empty set (0.00 sec)

3. What did you see instead (Required)

MySQL [test]> select * from t1 where (case when 0 <> 0 then (select c1 from t1) else 0 end) > 1; 
ERROR 1242 (21000): Subquery returns more than 1 row

MySQL [test]> explain select * from t1 where (case when 0 <> 0 then (select c1 from t1) else 0 end) > 1; 
ERROR 1242 (21000): Subquery returns more than 1 row

MySQL [test]> select * from t1 where (case when (select count(1) from t1) = 0 then (select c1 from t1) else 0 end) > 1; 
ERROR 1242 (21000): Subquery returns more than 1 row

4. What is your TiDB version? (Required)

= release-4.0

[solotzg]

@zanmato1984 PTAL.