feat(query): pretty format for explain

Signed-off-by: Enwei Jiao <enwei.jiao@zilliz.com>

query/src/sql/planner/format/display_plan.rs

@@ -21,7 +21,7 @@ impl Plan {
         match self {
             Plan::Query {
                 s_expr, metadata, ..
-            } => s_expr.to_format_tree(metadata).format_indent(),
+            } => s_expr.to_format_tree(metadata).format_pretty(),
             Plan::Explain { kind, plan } => {
                 let result = plan.format_indent()?;
                 Ok(format!("{:?}:\n{}", kind, result))

query/src/sql/planner/format/indent_format.rs

@@ -37,4 +37,25 @@ where T: Display
         }
         Ok(())
     }
+
+    /// format TreeNode in a pretty way
+    pub fn format_pretty(&self) -> Result<String> {
+        let mut buf = String::new();
+        self.format_pretty_impl(0, false, &mut buf)?;
+        Ok(buf)
+    }
+
+    fn format_pretty_impl(&self, indent: usize, is_last: bool, f: &mut String) -> Result<()> {
+        if indent == 0 {
+            writeln!(f, "{}", &self.payload).unwrap()
+        } else if is_last {
+            writeln!(f, "{}└── {}", "│   ".repeat(indent - 1), &self.payload).unwrap()
+        } else {
+            writeln!(f, "{}├── {}", "│   ".repeat(indent - 1), &self.payload).unwrap()
+        }
+        for (i, child) in self.children.iter().enumerate() {
+            child.format_pretty_impl(indent + 1, i == self.children.len() - 1, f)?;
+        }
+        Ok(())
+    }
 }

query/tests/it/sql/planner/format/mod.rs

@@ -184,4 +184,11 @@ fn test_format() {
     Scan: catalog.database.table
 "#;
     assert_eq!(result.as_str(), expect);
+    let pretty_result = tree.format_pretty().unwrap();
+    let pretty_expect = r#"HashJoin: INNER, build keys: [plus(col1, 123)], probe keys: [col2], join filters: []
+├── Filter: [true]
+│   └── Scan: catalog.database.table
+└── Scan: catalog.database.table
+"#;
+    assert_eq!(pretty_result.as_str(), pretty_expect);
 }