How to ignore type cast and nullability when convert RelNode to SqlNode?

[张鑫]

Hi all,

I want to translate a optimized sql by RelNode and then convert it into SqlNode 
so that I can get sql string to execute. After validation and optimization by 
HepPlanner, I got relNode. Then,


SqlNode sqlNode = RelToSqlConverter relToSqlConverter = new 
RelToSqlConverter(ClickHouseSqlDialect.DEFAULT).visitRoot(relNode).asStatement();

And the sql string of sqlNode is below,

```
Select
CAST(c1 AS `INT64`),
COUNT(*),
groupBitMap(c3)
...
```


My Original sql string is below,
```
Select
c1,
COUNT(c2),
COUNT(DISTINCT c3)
...
```


My expectation is like this,
```
Select
c1,
COUNT(c2),
groupBitMap(c3)
...
```


How can I achieve this by  ignore type cast and nullability etc.  to keep 
origin sql unchanged as much as possible?

Really thanks.