MohamedAbdeen21 commented on code in PR #11186:
URL: https://github.com/apache/datafusion/pull/11186#discussion_r1664830172


##########
datafusion/sql/tests/cases/plan_to_sql.rs:
##########
@@ -314,3 +310,78 @@ fn test_table_references_in_plan_to_sql() {
         "SELECT \"table\".id, \"table\".\"value\" FROM \"table\"",
     );
 }
+
+#[test]
+fn test_pretty_roundtrip() -> Result<()> {
+    let schema = Schema::new(vec![
+        Field::new("id", DataType::Utf8, false),
+        Field::new("age", DataType::Utf8, false),
+    ]);
+
+    let df_schema = DFSchema::try_from(schema)?;
+
+    let context = MockContextProvider::default();
+    let sql_to_rel = SqlToRel::new(&context);
+
+    let unparser = Unparser::default();
+
+    let sql_to_pretty_unparse = vec![
+        ("((id < 5) OR (age = 8))", "id < 5 OR age = 8"),
+        ("((id + 5) * (age * 8))", "(id + 5) * age * 8"),
+        ("(3 + (5 * 6) * 3)", "3 + 5 * 6 * 3"),
+        ("((3 * (5 + 6)) * 3)", "3 * (5 + 6) * 3"),
+        ("((3 AND (5 OR 6)) * 3)", "(3 AND (5 OR 6)) * 3"),
+        ("((3 + (5 + 6)) * 3)", "(3 + 5 + 6) * 3"),
+        ("((3 + (5 + 6)) + 3)", "3 + 5 + 6 + 3"),
+        ("3 + 5 + 6 + 3", "3 + 5 + 6 + 3"),
+        ("3 + (5 + (6 + 3))", "3 + 5 + 6 + 3"),
+        ("3 + ((5 + 6) + 3)", "3 + 5 + 6 + 3"),
+        ("(3 + 5) + (6 + 3)", "3 + 5 + 6 + 3"),
+        ("((3 + 5) + (6 + 3))", "3 + 5 + 6 + 3"),
+        (
+            "((id > 10) OR (age BETWEEN 10 AND 20))",
+            "id > 10 OR age BETWEEN 10 AND 20",
+        ),
+        (
+            "((id > 10) * (age BETWEEN 10 AND 20))",
+            "(id > 10) * (age BETWEEN 10 AND 20)",
+        ),
+        ("id - (age - 8)", "id - (age - 8)"),
+        ("((id - age) - 8)", "id - age - 8"),
+        ("(id OR (age - 8))", "id OR age - 8"),
+        ("(id / (age - 8))", "id / (age - 8)"),
+        ("((id / age) * 8)", "id / age * 8"),
+        ("((age + 10) < 20) IS TRUE", "(age + 10 < 20) IS TRUE"),
+        (
+            "(20 > (age + 5)) IS NOT FALSE",
+            "(20 > age + 5) IS NOT FALSE",
+        ),
+        ("(true AND false) IS FALSE", "(true AND false) IS FALSE"),
+        ("true AND (false IS FALSE)", "true AND false IS FALSE"),
+    ];
+
+    for (sql, pretty) in sql_to_pretty_unparse.iter() {
+        let sql_expr = Parser::new(&GenericDialect {})
+            .try_with_sql(sql)?
+            .parse_expr()?;
+        let expr =
+            sql_to_rel.sql_to_expr(sql_expr, &df_schema, &mut 
PlannerContext::new())?;
+        let round_trip_sql = unparser.expr_to_sql(&expr)?.to_string();
+        assert_eq!(pretty.to_string(), round_trip_sql);
+
+        // verify that the pretty string parses to the same underlying Expr
+        let pretty_sql_expr = Parser::new(&GenericDialect {})
+            .try_with_sql(pretty)?
+            .parse_expr()?;
+
+        let pretty_expr = sql_to_rel.sql_to_expr(
+            pretty_sql_expr,
+            &df_schema,
+            &mut PlannerContext::new(),
+        )?;
+
+        assert_eq!(expr.to_string(), pretty_expr.to_string());

Review Comment:
   But they can't be the same, the whole idea behind removing parenthesis is to 
maintain the final result regardless of which operations get executed first/has 
the parenthesis aka associativity.
   
   Here's an example from the tests:
   ` ("((id + 5) * (age * 8))", "(id + 5) * age * 8"),`
   
   Here's the tree of the first/original expr:
   ```
            *
           / \
          +   * 
        /  \  / \
         id  5 age 8
   ```
   
   And here's the cleaned one
   ```
               *
              / \
             *   8
           / \
          +   age
         / \
        id  5
   ```
   These obviously don't match, but it doesn't matter because multiplication is 
associative. Let (id+5) be x -> (x * age) * 8 is the exact same as x * (age * 
8). Almost all operators are associative except for division and subtraction, 
which are handled.
   
   Comparing the string representation seemed like the best solution.



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