[SPARK-27444][SQL] multi-select can be used in subquery

sql/catalyst/src/main/antlr4/org/apache/spark/sql/catalyst/parser/SqlBase.g4

@@ -81,8 +81,7 @@ singleTableSchema
 
 statement
     : query                                                            #statementDefault
-    | insertStatement                                                  #insertStatementDefault
-    | multiSelectStatement                                             #multiSelectStatementDefault
+    | ctes? dmlStatementNoWith                                         #dmlStatement
     | USE db=identifier                                                #use
     | CREATE database (IF NOT EXISTS)? identifier
         (COMMENT comment=STRING)? locationSpec?
@@ -356,14 +355,14 @@ resource
     : identifier STRING
     ;
 
-insertStatement
-    : (ctes)? insertInto queryTerm queryOrganization                                       #singleInsertQuery
-    | (ctes)? fromClause multiInsertQueryBody+                                             #multiInsertQuery
+dmlStatementNoWith
+    : insertInto queryTerm queryOrganization                                       #singleInsertQuery
+    | fromClause multiInsertQueryBody+                                             #multiInsertQuery
     ;
 
 queryNoWith
     : queryTerm queryOrganization                                               #noWithQuery
-    | fromClause selectStatement                                                #queryWithFrom
+    | fromClause selectStatement+                                               #queryWithFrom
     ;
 
 queryOrganization
@@ -379,10 +378,6 @@ multiInsertQueryBody
     : insertInto selectStatement
     ;
 
-multiSelectStatement
-    : (ctes)? fromClause selectStatement+                                                #multiSelect
-    ;
-
 selectStatement
     : querySpecification queryOrganization
     ;

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/parser/AstBuilder.scala

@@ -117,6 +117,12 @@ class AstBuilder(conf: SQLConf) extends SqlBaseBaseVisitor[AnyRef] with Logging
     query.optionalMap(ctx.ctes)(withCTE)
   }
 
+  override def visitDmlStatement(ctx: DmlStatementContext): AnyRef = withOrigin(ctx) {
+    val dmlStmt = plan(ctx.dmlStatementNoWith)
+    // Apply CTEs
+    dmlStmt.optionalMap(ctx.ctes)(withCTE)
+  }
+
   private def withCTE(ctx: CtesContext, plan: LogicalPlan): LogicalPlan = {
     val ctes = ctx.namedQuery.asScala.map { nCtx =>
       val namedQuery = visitNamedQuery(nCtx)
@@ -129,11 +135,21 @@ class AstBuilder(conf: SQLConf) extends SqlBaseBaseVisitor[AnyRef] with Logging
 
   override def visitQueryWithFrom(ctx: QueryWithFromContext): LogicalPlan = withOrigin(ctx) {
     val from = visitFromClause(ctx.fromClause)
-    validate(ctx.selectStatement.querySpecification.fromClause == null,
-      "Individual select statement can not have FROM cause as its already specified in the" +
-        " outer query block", ctx)
-    withQuerySpecification(ctx.selectStatement.querySpecification, from).
-      optionalMap(ctx.selectStatement.queryOrganization)(withQueryResultClauses)
+    val selects = ctx.selectStatement.asScala.map { select =>
+      validate(select.querySpecification.fromClause == null,
+        "This select statement can not have FROM cause as its already specified upfront",
+        select)
+
+      withQuerySpecification(select.querySpecification, from).
+        // Add organization statements.
+        optionalMap(select.queryOrganization)(withQueryResultClauses)
+    }
+    // If there are multiple SELECT just UNION them together into one query.
+    if (selects.length == 1) {
+      selects.head
+    } else {
+      Union(selects)
+    }
   }
 
   override def visitNoWithQuery(ctx: NoWithQueryContext): LogicalPlan = withOrigin(ctx) {
@@ -182,47 +198,21 @@ class AstBuilder(conf: SQLConf) extends SqlBaseBaseVisitor[AnyRef] with Logging
     }
 
     // If there are multiple INSERTS just UNION them together into one query.
-    val insertPlan = inserts match {
-      case Seq(query) => query
-      case queries => Union(queries)
-    }
-    // Apply CTEs
-    insertPlan.optionalMap(ctx.ctes)(withCTE)
-  }
-
-  override def visitMultiSelect(ctx: MultiSelectContext): LogicalPlan = withOrigin(ctx) {
-    val from = visitFromClause(ctx.fromClause)
-
-    // Build the insert clauses.
-    val selects = ctx.selectStatement.asScala.map {
-      body =>
-        validate(body.querySpecification.fromClause == null,
-          "Multi-select queries cannot have a FROM clause in their individual SELECT statements",
-          body)
-
-        withQuerySpecification(body.querySpecification, from).
-          // Add organization statements.
-          optionalMap(body.queryOrganization)(withQueryResultClauses)
-    }
-
-    // If there are multiple INSERTS just UNION them together into one query.
-    val selectUnionPlan = selects match {
-      case Seq(query) => query
-      case queries => Union(queries)
+    if (inserts.length == 1) {
+      inserts.head
+    } else {
+      Union(inserts)
     }
-    // Apply CTEs
-    selectUnionPlan.optionalMap(ctx.ctes)(withCTE)
   }
 
   /**
    * Create a logical plan for a regular (single-insert) query.
    */
   override def visitSingleInsertQuery(
       ctx: SingleInsertQueryContext): LogicalPlan = withOrigin(ctx) {
-    val insertPlan = withInsertInto(ctx.insertInto(),
-        plan(ctx.queryTerm).optionalMap(ctx.queryOrganization)(withQueryResultClauses))
-    // Apply CTEs
-    insertPlan.optionalMap(ctx.ctes)(withCTE)
+    withInsertInto(
+      ctx.insertInto(),
+      plan(ctx.queryTerm).optionalMap(ctx.queryOrganization)(withQueryResultClauses))
   }
 
   /**

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/parser/PlanParserSuite.scala

@@ -132,15 +132,19 @@ class PlanParserSuite extends AnalysisTest {
       table("a").select(star()).union(table("a").where('s < 10).select(star())))
     intercept(
       "from a select * select * from x where a.s < 10",
-      "Multi-select queries cannot have a FROM clause in their individual SELECT statements")
+      "This select statement can not have FROM cause as its already specified upfront")
     intercept(
       "from a select * from b",
-      "Individual select statement can not have FROM cause as its already specified in " +
-        "the outer query block")
+      "This select statement can not have FROM cause as its already specified upfront")
     assertEqual(
       "from a insert into tbl1 select * insert into tbl2 select * where s < 10",
       table("a").select(star()).insertInto("tbl1").union(
         table("a").where('s < 10).select(star()).insertInto("tbl2")))
+    assertEqual(
+      "select * from (from a select * select *)",
+      table("a").select(star())
+        .union(table("a").select(star()))
+        .as("__auto_generated_subquery_name").select(star()))
   }
 
   test("query organization") {