[GitHub] [flink] bowenli86 commented on a change in pull request #10110: [FLINK-14301][doc] add documentation for functions categories and new function resolution orders

[GitBox <gi...@apache.org>]

bowenli86 commented on a change in pull request #10110: [FLINK-14301][doc] add documentation for functions categories and new function resolution orders
URL: https://github.com/apache/flink/pull/10110#discussion_r343907309
 
 

 ##########
 File path: docs/dev/table/functions/index.md
 ##########
 @@ -0,0 +1,96 @@
+---
+title: "Functions"
+nav-id: table_functions
+nav-parent_id: tableapi
+nav-pos: 116
+is_beta: true
+nav-show_overview: true
+---
+<!--
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements.  See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership.  The ASF licenses this file
+to you 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.
+-->
+
+Flink Table API & SQL empowers users to do data transformations with functions.
+
+Types of Functions
+------------------
+
+There are two dimensions to classify functions in Flink.
+
+One dimension is system (or built-in) functions v.s. catalog functions. System functions have no namespace and can be
+referenced with just their names. Catalog functions belong to a catalog and database therefore they have catalog and database
+namespaces, they can be referenced by either fully/partially qualified name (`catalog.db.func` or `db.func`) or just the
+function name.
+
+The other dimension is temporary functions v.s. persistent functions. Temporary functions are volatile and only live up to
+ lifespan of a session, they are always created by users. Persistent functions live across lifespan of sessions, they are either
+ provided by the system or persisted in catalogs.
+ 
+The two dimensions give Flink users 4 categories of functions:
+
+1. Temporary system functions
+2. System functions
+3. Temporary catalog functions
+4. Catalog functions
+
 
 Review comment:
   I actually feel they are related to help users understand resolution order below. Maybe I should have mentioned that in resolution order, system functions always precede catalog's and temporary functions always precede persistent on its own dimension

----------------------------------------------------------------
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.
 
For queries about this service, please contact Infrastructure at:
users@infra.apache.org


With regards,
Apache Git Services