[GitHub] [arrow-datafusion] xudong963 commented on pull request #1621: feat: Support Substring(str [from int] [for int])

[GitBox <gi...@apache.org>]

xudong963 commented on pull request #1621:
URL: https://github.com/apache/arrow-datafusion/pull/1621#issuecomment-1017702031


   Thanks @ovr !
   
   Lol, I also have just done exactly this for https://github.com/apache/arrow-datafusion/issues/175
   
   Our idea is same, transfer `Expr::Substring` to `Expr::Function`
   ```rust
                   let sql_expr = SQLExpr::Function(Function {
                       name: ObjectName(
                           [Ident {
                               value: "substr".to_string(),
                               quote_style: None,
                           }]
                           .to_vec(),
                       ),
                       args: [
                           FunctionArg::Unnamed(*expr.clone()),
                           FunctionArg::Unnamed(from_expr),
                           FunctionArg::Unnamed(for_expr),
                       ]
                       .to_vec(),
                       over: None,
                       distinct: false,
                   });
                   dbg!(schema.clone());
                   self.sql_expr_to_logical_expr(&sql_expr, schema)
   ```
   I'll help to review after getting up


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