[SPARK-13924][SQL] officially support multi-insert

## What changes were proposed in this pull request?

There is a feature of hive SQL called multi-insert. For example:
```
FROM src
INSERT OVERWRITE TABLE dest1
SELECT key + 1
INSERT OVERWRITE TABLE dest2
SELECT key WHERE key > 2
INSERT OVERWRITE TABLE dest3
SELECT col EXPLODE(arr) exp AS col
...
```

We partially support it currently, with some limitations: 1) WHERE can't reference columns produced by LATERAL VIEW. 2) It's not executed eagerly, i.e. `sql("...multi-insert clause...")` won't take place right away like other commands, e.g. CREATE TABLE.

This PR removes these limitations and make us fully support multi-insert.

## How was this patch tested?

new tests in `SQLQuerySuite`

Author: Wenchen Fan <wenchen@databricks.com>

Closes #11754 from cloud-fan/lateral-view.

1 files changed, 18 insertions, 9 deletions

diff --git a/sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala b/sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala
index 969fcdf428..ac2ca3c5a3 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/Dataset.scala
@@ -134,15 +134,24 @@ class Dataset[T] private[sql](
     this(sqlContext, sqlContext.executePlan(logicalPlan), encoder)
   }
 
-  @transient protected[sql] val logicalPlan: LogicalPlan = queryExecution.logical match {
-    // For various commands (like DDL) and queries with side effects, we force query optimization to
-    // happen right away to let these side effects take place eagerly.
-    case _: Command |
-         _: InsertIntoTable |
-         _: CreateTableUsingAsSelect =>
-      LogicalRDD(queryExecution.analyzed.output, queryExecution.toRdd)(sqlContext)
-    case _ =>
-      queryExecution.analyzed
+  @transient protected[sql] val logicalPlan: LogicalPlan = {
+    def hasSideEffects(plan: LogicalPlan): Boolean = plan match {
+      case _: Command |
+           _: InsertIntoTable |
+           _: CreateTableUsingAsSelect => true
+      case _ => false
+    }
+
+    queryExecution.logical match {
+      // For various commands (like DDL) and queries with side effects, we force query execution
+      // to happen right away to let these side effects take place eagerly.
+      case p if hasSideEffects(p) =>
+        LogicalRDD(queryExecution.analyzed.output, queryExecution.toRdd)(sqlContext)
+      case Union(children) if children.forall(hasSideEffects) =>
+        LogicalRDD(queryExecution.analyzed.output, queryExecution.toRdd)(sqlContext)
+      case _ =>
+        queryExecution.analyzed
+    }
   }
 
   /**