[GitHub] [spark] GuoPhilipse commented on a change in pull request #29056: [SPARK-31753][SQL][DOCS][WIP]Add missing keywords

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

GuoPhilipse commented on a change in pull request #29056:
URL: https://github.com/apache/spark/pull/29056#discussion_r452572268



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File path: docs/sql-ref-syntax-qry-select-case.md
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@@ -0,0 +1,115 @@
+---
+layout: global
+title: CASE Clause
+displayTitle: CASE Clause
+license: |
+  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.
+---
+
+### Description
+
+`CASE` clause uses rule to return specific result based on the specified condition.
+
+### Syntax
+
+```sql
+CASE { WHEN boolean_expression THEN then_expression }{ WHEN boolean_expression THEN then_expression } [ , ... ] [ ELSE else_expression ] END
+
+CASE expression { WHEN boolean_expression THEN then_expression }{ WHEN boolean_expression THEN then_expression } [ , ... ] [ ELSE else_expression ] END
+```
+
+### Parameters
+    
+* **WHEN**
+
+    Specific a boolean condition ,under which to return the `THEN` result, `WHEN` must exist in `CASE` clause.
+    
+* **THEN**
+
+    Specific a result base the `WHEN` condition, `THEN` must exist in `CASE` clause.
+    
+* **ELSE**
+
+    Specific a default result for the `CASE` rules, it is optional, if user don't use else then the `CASE` will not have default result.
+    
+* **END**
+
+    Key words to finish a case clause, `END` must exist in `CASE` clause.
+    
+* **boolean_expression**
+
+    Specific specified condition, it should be boolean type.
+    
+* **then_expression**
+
+    Specific the then expression based on the `boolean_expression` condition, `then_expression` and `else_expression` should all be same type or coercible to a common type.
+    
+* **else_expression**
+
+    Specific the default expression, `then_expression` and `else_expression` should all be same type or coercible to a common type.
+    
+### Examples
+
+```sql
+CREATE TABLE person (id INT, name STRING, age INT);
+INSERT INTO person VALUES
+    (100, 'John', 30),
+    (200, 'Mary', NULL),
+    (300, 'Mike', 80),
+    (400, 'Dan',  50),
+    (500, 'Evan_w', 16);
+
+select id, case when id > 200 then 'bigger' else 'small' end from person;

Review comment:
       Thanks@dongjoon-hyun ,will improve it next commit.




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