[GitHub] [spark] huaxingao commented on a change in pull request #28237: [SPARK-31465][SQL][DOCS] Document Literal in SQL Reference

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huaxingao commented on a change in pull request #28237:
URL: https://github.com/apache/spark/pull/28237#discussion_r411082047



##########
File path: docs/sql-ref-literals.md
##########
@@ -0,0 +1,505 @@
+---
+layout: global
+title: Literals
+displayTitle: Literals
+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.
+---
+
+A literal (also known as a constant) represents a fixed data value. Spark SQL 
supports the following literals:
+
+ * [String Literal](#string-literal)
+ * [Null Literal](#null-literal)
+ * [Boolean Literal](#boolean-literal)
+ * [Numeric Literal](#numeric-literal)
+ * [Datetime Literal](#datetime-literal)
+ * [Interval Literal](#interval-literal)
+
+### String Literal
+
+A string literal is used to specify a character string value.
+
+#### Syntax
+
+{% highlight sql %}
+'c [ ... ]' | "c [ ... ]"
+{% endhighlight %}
+
+#### <em>Parameters</em>
+
+<dl>
+  <dt><code><em>c</em></code></dt>
+  <dd>
+    One character from the character set. Use <code>\</code> to escape special 
characters.
+  </dd>
+</dl>
+
+#### <em>Examples</em>
+
+{% highlight sql %}
+SELECT 'Hello, World!' AS col;
+  +-------------+
+  |          col|
+  +-------------+
+  |Hello, World!|
+  +-------------+
+
+SELECT "SPARK SQL" AS col;
+  +---------+
+  |      col|
+  +---------+
+  |Spark SQL|
+  +---------+
+
+SELECT SELECT 'it\'s $10.' AS col;
+  +---------+
+  |      col|
+  +---------+
+  |It's $10.|
+  +---------+
+{% endhighlight %}
+
+### Null Literal
+
+A null literal is used to specify a null value.
+
+#### Syntax
+
+{% highlight sql %}
+NULL
+{% endhighlight %}
+
+#### Examples
+
+{% highlight sql %}
+SELECT NULL AS col;
+  +----+
+  | col|
+  +----+
+  |NULL|
+  +----+
+{% endhighlight %}
+
+### Boolean Literal
+
+A boolean literal is used to specify a boolean value.
+
+#### Syntax
+
+{% highlight sql %}
+TRUE | FALSE
+{% endhighlight %}
+
+#### Examples
+
+{% highlight sql %}
+SELECT TRUE AS col;
+  +----+
+  | col|
+  +----+
+  |true|
+  +----+
+{% endhighlight %}
+
+### Numeric Literal
+
+A numeric literal is used to specify a fixed or floating-point number.
+
+#### Integer Literal
+
+#### Syntax

Review comment:
       I prefer not to add. The font seems to small if add one more #
   <img width="825" alt="Screen Shot 2020-04-19 at 9 12 52 PM" 
src="https://user-images.githubusercontent.com/13592258/79713482-c030bb80-8282-11ea-992f-eadad975f4c2.png";>
   vs
   <img width="793" alt="Screen Shot 2020-04-19 at 9 12 06 PM" 
src="https://user-images.githubusercontent.com/13592258/79713488-c3c44280-8282-11ea-8af2-17efcb897b06.png";>
   




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