Function simplify_concat

datafusion/functions/src/string/concat.rs:310–392

(args: Vec<Expr>)

}

pub(crate) fn simplify_concat(args: Vec<Expr>) -> Result<ExprSimplifyResult> {
    let mut new_args = Vec::with_capacity(args.len());
    let mut contiguous_scalar = "".to_string();

    let return_type = {
        let data_types: Vec<_> = args
            .iter()
            .filter_map(|expr| match expr {
                Expr::Literal(l, _) => Some(l.data_type()),
                _ => None,
            })
            .collect();
        ConcatFunc::new().return_type(&data_types)
    }?;

    for arg in args.clone() {
        match arg {
            Expr::Literal(ScalarValue::Utf8(None), _) => {}
            Expr::Literal(ScalarValue::LargeUtf8(None), _) => {}
            Expr::Literal(ScalarValue::Utf8View(None), _) => {}

            // filter out `null` args
            // All literals have been converted to Utf8 or LargeUtf8 in type_coercion.
            // Concatenate it with the `contiguous_scalar`.
            Expr::Literal(ScalarValue::Utf8(Some(v)), _) => {
                contiguous_scalar += &v;
            }
            Expr::Literal(ScalarValue::LargeUtf8(Some(v)), _) => {
                contiguous_scalar += &v;
            }
            Expr::Literal(ScalarValue::Utf8View(Some(v)), _) => {
                contiguous_scalar += &v;
            }

            Expr::Literal(x, _) => {
                return internal_err!(
                    "The scalar {x} should be casted to string type during the type coercion."
                );
            }
            // If the arg is not a literal, we should first push the current `contiguous_scalar`
            // to the `new_args` (if it is not empty) and reset it to empty string.
            // Then pushing this arg to the `new_args`.
            arg => {
                if !contiguous_scalar.is_empty() {
                    match return_type {
                        DataType::Utf8 => new_args.push(lit(contiguous_scalar)),
                        DataType::LargeUtf8 => new_args
                            .push(lit(ScalarValue::LargeUtf8(Some(contiguous_scalar)))),
                        DataType::Utf8View => new_args
                            .push(lit(ScalarValue::Utf8View(Some(contiguous_scalar)))),
                        _ => unreachable!(),
                    }
                    contiguous_scalar = "".to_string();
                }
                new_args.push(arg);
            }
        }
    }