qstommyshu commented on code in PR #15736:
URL: https://github.com/apache/datafusion/pull/15736#discussion_r2047845110


##########
datafusion/sql/src/parser.rs:
##########
@@ -469,9 +473,101 @@ impl<'a> DFParser<'a> {
                     }
                     _ => {
                         // use sqlparser-rs parser
-                        Ok(Statement::Statement(Box::from(
-                            self.parser.parse_statement()?,
-                        )))
+                        let mut stmt = self.parser.parse_statement()?;
+
+                        use sqlparser::ast::{DataType, Expr, Spanned, Value};
+
+                        if let sqlparser::ast::Statement::Query(query) = &mut 
stmt {
+                            if let sqlparser::ast::SetExpr::Select(select) =
+                                &mut *query.body
+                            {
+                                // if missing from
+                                if select.from.is_empty() {
+                                    let mut new_projection = Vec::new();
+
+                                    for expr in &select.projection {
+                                        match expr {
+                                            
sqlparser::ast::SelectItem::UnnamedExpr(
+                                                cast_expr,
+                                            ) => {
+                                                if let Expr::Cast {
+                                                    expr: inner_expr,
+                                                    data_type,
+                                                    ..
+                                                } = cast_expr
+                                                {
+                                                    let inner_str = match 
&**inner_expr {
+                                                            
Expr::Value(sqlparser::ast::ValueWithSpan { value: 
Value::SingleQuotedString(s), .. }) => {
+                                                                
format!("'{}'", s)
+                                                            },
+                                                            
Expr::Value(sqlparser::ast::ValueWithSpan { value: Value::Number(n, _), .. }) 
=> {
+                                                                n.clone()
+                                                            },
+                                                            // TODO: need to 
take care of other types of values, like TimeStamp, etc...
+                                                            _ => 
format!("{:?}", inner_expr),
+                                                        };
+
+                                                    // get cast to type string
+                                                    let type_str = match 
data_type {
+                                                        DataType::Int(_) => 
"INT",
+                                                        DataType::BigInt(_) => 
"BIGINT",
+                                                        DataType::SmallInt(_) 
=> {
+                                                            "SMALLINT"
+                                                        }
+                                                        DataType::Boolean => 
"BOOLEAN",
+                                                        DataType::Varchar(_) 
=> "VARCHAR",
+                                                        DataType::Float(_) => 
"FLOAT",
+                                                        DataType::Double(_) => 
"DOUBLE",
+                                                        DataType::Text => 
"TEXT",
+                                                        // TODO: need to 
support more DataType, probably use an Extension Trait

Review Comment:
   We need to support a full list of enum elements for `DataType` here, this 
`DataType` comes from an external library. This probably means everything we 
update this API, we need to make accommodation as well.
   
   Or we can look into using `strum` crate to auto derive `ToString` for all 
`DataType`, we are currently using it for the `datafusion proto` crate.



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