Function placeholder

datafusion/expr/src/expr_fn.rs:125–130

Create placeholder value that will be filled in (such as `$1`) Note the parameter type can be inferred using [`Expr::infer_placeholder_types`] # Example ```rust # use datafusion_expr::{placeholder}; let p = placeholder("$1"); // $1, refers to parameter 1 assert_eq!(p.to_string(), "$1") ```

(id: impl Into<String>)

/// assert_eq!(p.to_string(), "$1")
/// ```
pub fn placeholder(id: impl Into<String>) -> Expr {
    Expr::Placeholder(Placeholder {
        id: id.into(),
        field: None,
    })
}

/// Create an '*' [`Expr::Wildcard`] expression that matches all columns
///