feat: Frontend show tables and databases (#504)

* feat: Frontend show tables and databases

Co-authored-by: luofucong <luofucong@greptime.com>

src/catalog/src/lib.rs

@@ -80,6 +80,8 @@ pub trait CatalogManager: CatalogList {
     async fn register_system_table(&self, request: RegisterSystemTableRequest)
         -> error::Result<()>;
 
+    fn schema(&self, catalog: &str, schema: &str) -> Result<Option<SchemaProviderRef>>;
+
     /// Returns the table by catalog, schema and table name.
     fn table(&self, catalog: &str, schema: &str, table_name: &str) -> Result<Option<TableRef>>;
 }

src/catalog/src/local/manager.rs

@@ -33,7 +33,7 @@ use crate::tables::SystemCatalog;
 use crate::{
     format_full_table_name, handle_system_table_request, CatalogList, CatalogManager,
     CatalogProvider, CatalogProviderRef, RegisterSchemaRequest, RegisterSystemTableRequest,
-    RegisterTableRequest, SchemaProvider,
+    RegisterTableRequest, SchemaProvider, SchemaProviderRef,
 };
 
 /// A `CatalogManager` consists of a system catalog and a bunch of user catalogs.
@@ -379,6 +379,15 @@ impl CatalogManager for LocalCatalogManager {
         Ok(())
     }
 
+    fn schema(&self, catalog: &str, schema: &str) -> Result<Option<SchemaProviderRef>> {
+        self.catalogs
+            .catalog(catalog)?
+            .context(CatalogNotFoundSnafu {
+                catalog_name: catalog,
+            })?
+            .schema(schema)
+    }
+
     fn table(
         &self,
         catalog_name: &str,

src/catalog/src/local/memory.rs

@@ -89,6 +89,15 @@ impl CatalogManager for MemoryCatalogManager {
         unimplemented!()
     }
 
+    fn schema(&self, catalog: &str, schema: &str) -> Result<Option<SchemaProviderRef>> {
+        let catalogs = self.catalogs.read().unwrap();
+        if let Some(c) = catalogs.get(catalog) {
+            c.schema(schema)
+        } else {
+            Ok(None)
+        }
+    }
+
     fn table(&self, catalog: &str, schema: &str, table_name: &str) -> Result<Option<TableRef>> {
         let c = self.catalogs.read().unwrap();
         let catalog = if let Some(c) = c.get(catalog) {

src/catalog/src/remote/manager.rs

@@ -414,6 +414,14 @@ impl CatalogManager for RemoteCatalogManager {
         Ok(())
     }
 
+    fn schema(&self, catalog: &str, schema: &str) -> Result<Option<SchemaProviderRef>> {
+        self.catalog(catalog)?
+            .context(CatalogNotFoundSnafu {
+                catalog_name: catalog,
+            })?
+            .schema(schema)
+    }
+
     fn table(
         &self,
         catalog_name: &str,