maropu commented on a change in pull request #26970: [SPARK-28825][SQL][DOC]
Documentation for Explain Command
URL: https://github.com/apache/spark/pull/26970#discussion_r361028626
##########
File path: docs/sql-ref-syntax-qry-explain.md
##########
@@ -19,4 +19,126 @@ license: |
limitations under the License.
---
-**This page is under construction**
+### Description
+
+The `EXPLAIN` statement provides the execution plan for the statement.
+By default, `EXPLAIN` provides information about the physical plan.
+`EXPLAIN` does not support `DESCRIBE TABLE` statement.
+
+
+### Syntax
+{% highlight sql %}
+EXPLAIN [EXTENDED | CODEGEN | COST | FORMATTED] statement
+{% endhighlight %}
+
+### Parameters
+
+<dl>
+ <dt><code><em>EXTENDED</em></code></dt>
+ <dd>Generates Parsed Logical Plan, Analyzed Logical Plan, Optimized Logical
Plan and Physical Plan.
+ Parsed Logical plan is a unresolved plan that extracted from the query.
+ Analyzed logical plans transforms which translates UnresolvedAttribute and
UnresolvedRelation into fully typed objects.
+ The optimized logical plan transforms through a set of optimization rules,
resulting in the Physical plan.
+ </dd>
+</dl>
+
+<dl>
+ <dt><code><em>CODEGEN</em></code></dt>
+ <dd>Generates code for the statement, if any and a Physical Plan.</dd>
+</dl>
+
+<dl>
+ <dt><code><em>COST</em></code></dt>
+ <dd>If plan node statistics are available, generates a logical plan and the
statistics.</dd>
+</dl>
+
+<dl>
+ <dt><code><em>FORMATTED</em></code></dt>
+ <dd>Generates two sections: a physical plan outline and node details.</dd>
+</dl>
+
+### Examples
+{% highlight sql %}
+
+-- Using Extended
+
+EXPLAIN EXTENDED select * from emp;
++----------------------------------------------------+
+| plan |
++----------------------------------------------------+
+| == Parsed Logical Plan ==
+'Project [*]
++- 'UnresolvedRelation [emp]
+
+== Analyzed Logical Plan ==
+id: int
+Project [id#0]
++- SubqueryAlias `default`.`emp`
+ +- Relation[id#0] parquet
+
+== Optimized Logical Plan ==
+Relation[id#0] parquet
+
+== Physical Plan ==
+*(1) ColumnarToRow
++- FileScan parquet default.emp[id#0] Batched: true, DataFilters: [], Format:
Parquet, Location:
InMemoryFileIndex[file:/home/root1/Spark/spark/spark-warehouse/emp],
PartitionFilters: [], PushedFilters: [], ReadSchema: struct<id:int>
+ |
++----------------------------------------------------+
+
+--Default Output
+
+EXPLAIN select * from emp;
++----------------------------------------------------+
+| plan |
++----------------------------------------------------+
+| == Physical Plan ==
+*(1) ColumnarToRow
++- FileScan parquet default.emp[id#0] Batched: true, DataFilters: [], Format:
Parquet, Location:
InMemoryFileIndex[file:/home/root1/Spark/spark/spark-warehouse/emp],
PartitionFilters: [], PushedFilters: [], ReadSchema: struct<id:int>
+
+ |
++----------------------------------------------------+
+
+-- Using Cost
+EXPLAIN COST select * from emp;
++----------------------------------------------------+
+| plan |
++----------------------------------------------------+
+| == Optimized Logical Plan ==
+Relation[id#5] parquet, Statistics(sizeInBytes=421.0 B)
+
+== Physical Plan ==
+*(1) ColumnarToRow
++- FileScan parquet default.emp[id#5] Batched: true, DataFilters: [], Format:
Parquet, Location:
InMemoryFileIndex[file:/home/root1/Spark/spark/spark-warehouse/emp],
PartitionFilters: [], PushedFilters: [], ReadSchema: struct<id:int>
+
+ |
++----------------------------------------------------+
+
+--Using Formatted
+
+EXPLAIN FORMATTED select * from emp;
++----------------------------------------------------+
+| plan |
++----------------------------------------------------+
+| == Physical Plan ==
+* ColumnarToRow (2)
++- Scan parquet default.emp (1)
+
+
+(1) Scan parquet default.emp
+Output: [id#5]
+Batched: true
+Location: InMemoryFileIndex [file:/home/root1/Spark/spark/spark-warehouse/emp]
+ReadSchema: struct<id:int>
+
+(2) ColumnarToRow [codegen id : 1]
+Input: [id#5]
+
+ |
++----------------------------------------------------+
+
+
+-- Using CODEGEN
+
+EXPLAIN CODEGEN select * from emp;
Review comment:
I think we don't need this CODEGEN example.
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