feat: add table info (#323)

* refactor: add table_info method for Table trait

* feat: add table_info method to Table trait

* test: add more unit test

* fix: impl table_info for SystemTable

* test: fix failing test

src/sql/Cargo.toml

@@ -5,6 +5,7 @@ edition = "2021"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+catalog = { path = "../catalog" }
 common-error = { path = "../common/error" }
 common-time = { path = "../common/time" }
 datatypes = { path = "../datatypes" }

src/sql/src/statements.rs

@@ -7,6 +7,7 @@ pub mod statement;
 
 use std::str::FromStr;
 
+use catalog::{DEFAULT_CATALOG_NAME, DEFAULT_SCHEMA_NAME};
 use common_time::Timestamp;
 use datatypes::prelude::ConcreteDataType;
 use datatypes::schema::{ColumnDefaultConstraint, ColumnSchema};
@@ -24,14 +25,16 @@ use crate::error::{
 
 /// Converts maybe fully-qualified table name (`<catalog>.<schema>.<table>` or `<table>` when
 /// catalog and schema are default) to tuple.
-pub fn table_idents_to_full_name(
-    obj_name: &ObjectName,
-) -> Result<(Option<String>, Option<String>, String)> {
+pub fn table_idents_to_full_name(obj_name: &ObjectName) -> Result<(String, String, String)> {
     match &obj_name.0[..] {
-        [table] => Ok((None, None, table.value.clone())),
+        [table] => Ok((
+            DEFAULT_CATALOG_NAME.to_string(),
+            DEFAULT_SCHEMA_NAME.to_string(),
+            table.value.clone(),
+        )),
         [catalog, schema, table] => Ok((
-            Some(catalog.value.clone()),
-            Some(schema.value.clone()),
+            catalog.value.clone(),
+            schema.value.clone(),
             table.value.clone(),
         )),
         _ => error::InvalidSqlSnafu {