bug: downcast column error

[zhang2014]

Search before asking

• I had searched in the issues and found no similar issues.

Version

main branch

mysql> select version();
+--------------------------------------------------------------------------------------+
| version()                                                                            |
+--------------------------------------------------------------------------------------+
| 8.0.26-v0.7.65-nightly-cae12e2-simd(rust-1.63.0-nightly-2022-06-21T01:36:27.065955Z) |
+--------------------------------------------------------------------------------------+
1 row in set (0.03 sec)

What's Wrong?

mysql> SELECT count() FROM numbers(1000) GROUP BY uuid();
ERROR 1105 (HY000): Code: 1058, displayText = downcast column error, column type: "Const(String)", expected column: "common_datavalues::columns::string::StringColumn" (while in processor thread 0).

How to Reproduce?

No response

Are you willing to submit PR?

• Yes I am willing to submit a PR!

[leiysky]

I encountered this bug too, the root cause is SingleString hash method won't check Const and Nullable column.

https://github.com/datafuselabs/databend/blob/7d46a582a44e29f1dec988908102894c89d0aefc/common/datablocks/src/kernels/data_block_group_by_hash.rs#L208-L223

cc @sundy-li

[zhang2014]

Why GROUP BY uuid() is const column?

[sundy-li]

Now uuid function generates const column. Maybe we should modify and set uuid value to each row.