[QUESTION] How many times should be the function `create_name` called when executing a query?

[HaoYang670]

Describe the bug
A clear and concise description of what the bug is.
Related to this function: https://github.com/apache/arrow-datafusion/blob/master/datafusion/expr/src/expr.rs#L951

To Reproduce
I add println here to check if the function is called:

/// Returns a readable name of an expression based on the input schema.
/// This function recursively transverses the expression for names such as "CAST(a > 2)".
fn create_name(e: &Expr) -> Result<String> {
    println!("create name for e");

note that the println command doesn't get the name of e to avoid recursive function calls.

Then I ran a really simple query in the datafusion-cli, and got the following result:

DataFusion CLI v13.0.0
❯ select 1;
create name for e
create name for e
create name for e
create name for e
create name for e
create name for e
create name for e
create name for e
create name for e
create name for e
create name for e
create name for e
create name for e
create name for e
create name for e
create name for e
create name for e
create name for e
+----------+
| Int64(1) |
+----------+
| 1        |
+----------+
1 row in set. Query took 0.004 seconds.

It is a little weird to me that the function create_name is called 18 times.

I also tested by constructing the expression directly:

    #[test]
    fn my_fail_test() {
        let expr = lit(1);
        // make the test failed, so that we can see the content from `println`
        assert_eq!("UINT(2)", expr.display_name().unwrap())
    }

, and this works fine:

running 1 test
create name for e
thread 'expr::test::my_fail_test' panicked at 'assertion failed: `(left == right)`
  left: `"UINT(2)"`,
 right: `"Int32(1)"`', datafusion/expr/src/expr.rs:1255:9

Expected behavior
I guess the function create_name should only be called once for each expression.

Additional context
Add any other context about the problem here.

[comphead]

There are couple of ways to come to create_name

• aliasing not qualified cols, this works good, 2 calls only
• display_name() which calls create_name and the first one gets called everywhere

[HaoYang670]

Thank you, @comphead, for your explanation. It makes sense now. I'll close the ticket.