feat: support information_schema.views (risingwavelabs#12045)

Author: Tao Wu

src/frontend/src/catalog/system_catalog/information_schema/mod.rs

@@ -14,6 +14,8 @@
 
 pub mod columns;
 pub mod tables;
+pub mod views;
 
 pub use columns::*;
 pub use tables::*;
+pub use views::*;

src/frontend/src/catalog/system_catalog/information_schema/views.rs

@@ -0,0 +1,45 @@
+// Copyright 2023 RisingWave Labs
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use std::sync::LazyLock;
+
+use risingwave_common::catalog::INFORMATION_SCHEMA_SCHEMA_NAME;
+use risingwave_common::types::DataType;
+
+use crate::catalog::system_catalog::BuiltinView;
+
+/// The view `views` contains all views defined in the current database. Only those views
+/// are shown that the current user has access to (by way of being the owner or having
+/// some privilege).
+/// Ref: [`https://www.postgresql.org/docs/current/infoschema-views.html`]
+///
+/// In RisingWave, `views` contains information about defined views.
+pub static INFORMATION_SCHEMA_VIEWS: LazyLock<BuiltinView> = LazyLock::new(|| BuiltinView {
+    name: "views",
+    schema: INFORMATION_SCHEMA_SCHEMA_NAME,
+    columns: &[
+        (DataType::Varchar, "table_catalog"),
+        (DataType::Varchar, "table_schema"),
+        (DataType::Varchar, "table_name"),
+        (DataType::Varchar, "view_definition"),
+    ],
+    sql: "SELECT CURRENT_DATABASE() AS table_catalog, \
+                s.name AS table_schema, \
+                v.name AS table_name, \
+                v.definition AS view_definition \
+            FROM rw_catalog.rw_views v \
+            JOIN rw_catalog.rw_schemas s ON v.schema_id = s.id \
+        ORDER BY table_schema, table_name"
+        .to_string(),
+});

src/frontend/src/catalog/system_catalog/mod.rs

@@ -377,6 +377,7 @@ prepare_sys_catalog! {
     { BuiltinCatalog::View(&PG_DEPEND) },
     { BuiltinCatalog::View(&INFORMATION_SCHEMA_COLUMNS) },
     { BuiltinCatalog::View(&INFORMATION_SCHEMA_TABLES) },
+    { BuiltinCatalog::View(&INFORMATION_SCHEMA_VIEWS) },
     { BuiltinCatalog::Table(&RW_DATABASES), read_rw_database_info },
     { BuiltinCatalog::Table(&RW_SCHEMAS), read_rw_schema_info },
     { BuiltinCatalog::Table(&RW_USERS), read_rw_user_info },