Allow to use case-insensitive column names

[zhouyuan]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
Spark is case-insensitive column names inside one query. E.g
select col_a, count(col_A), avg(col_b) from table group by col_A

Describe the solution you'd like
align with spark, allow using case-insensitive names

Describe alternatives you've considered
N/A

Additional context
N/A