[SPARK-21335][SQL] support un-aliased subquery

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

@@ -751,15 +751,17 @@ class AstBuilder extends SqlBaseBaseVisitor[AnyRef] with Logging {
    * hooks.
    */
   override def visitAliasedQuery(ctx: AliasedQueryContext): LogicalPlan = withOrigin(ctx) {
-    // The unaliased subqueries in the FROM clause are disallowed. Instead of rejecting it in
-    // parser rules, we handle it here in order to provide better error message.
-    if (ctx.strictIdentifier == null) {
-      throw new ParseException("The unaliased subqueries in the FROM clause are not supported.",
-        ctx)
+    val alias = if (ctx.strictIdentifier == null) {
+      // For un-aliased subqueries, ues a default alias name that is not likely to conflict with
+      // normal subquery names, so that parent operators can only access the columns in subquery by
+      // unqualified names. Users can still use this special qualifier to access columns if they
+      // know it, but that's not recommended.
+      "_auto_generated_subquery_name"
+    } else {
+      ctx.strictIdentifier.getText
     }
 
-    aliasPlan(ctx.strictIdentifier,
-      plan(ctx.queryNoWith).optionalMap(ctx.sample)(withSample))
+    SubqueryAlias(alias, plan(ctx.queryNoWith).optionalMap(ctx.sample)(withSample))
   }
 
   /**

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/logical/LogicalPlan.scala

@@ -253,7 +253,7 @@ abstract class LogicalPlan
 
       // More than one match.
       case ambiguousReferences =>
-        val referenceNames = ambiguousReferences.map(_._1).mkString(", ")
+        val referenceNames = ambiguousReferences.map(_._1.qualifiedName).mkString(", ")
         throw new AnalysisException(
           s"Reference '$name' is ambiguous, could be: $referenceNames.")
     }

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

@@ -450,19 +450,6 @@ class PlanParserSuite extends AnalysisTest {
         |      (select id from t0)) as u_1
       """.stripMargin,
       plan.union(plan).union(plan).as("u_1").select('id))
-
-  }
-
-  test("aliased subquery") {
-    val errMsg = "The unaliased subqueries in the FROM clause are not supported"
-
-    assertEqual("select a from (select id as a from t0) tt",
-      table("t0").select('id.as("a")).as("tt").select('a))
-    intercept("select a from (select id as a from t0)", errMsg)
-
-    assertEqual("from (select id as a from t0) tt select a",
-      table("t0").select('id.as("a")).as("tt").select('a))
-    intercept("from (select id as a from t0) select a", errMsg)
   }
 
   test("scalar sub-query") {

sql/core/src/test/resources/sql-tests/inputs/group-by.sql

@@ -34,7 +34,7 @@ SELECT SKEWNESS(a), KURTOSIS(a), MIN(a), MAX(a), AVG(a), VARIANCE(a), STDDEV(a),
 FROM testData;
 
 -- Aggregate with foldable input and multiple distinct groups.
-SELECT COUNT(DISTINCT b), COUNT(DISTINCT b, c) FROM (SELECT 1 AS a, 2 AS b, 3 AS c) t GROUP BY a;
+SELECT COUNT(DISTINCT b), COUNT(DISTINCT b, c) FROM (SELECT 1 AS a, 2 AS b, 3 AS c) GROUP BY a;
 
 -- Aliases in SELECT could be used in GROUP BY
 SELECT a AS k, COUNT(b) FROM testData GROUP BY k;

sql/core/src/test/resources/sql-tests/inputs/limit.sql

@@ -21,7 +21,7 @@ SELECT * FROM testdata LIMIT true;
 SELECT * FROM testdata LIMIT 'a';
 
 -- limit within a subquery
-SELECT * FROM (SELECT * FROM range(10) LIMIT 5) t WHERE id > 3;
+SELECT * FROM (SELECT * FROM range(10) LIMIT 5) WHERE id > 3;
 
 -- limit ALL
 SELECT * FROM testdata WHERE key < 3 LIMIT ALL;

sql/core/src/test/resources/sql-tests/inputs/string-functions.sql

@@ -7,7 +7,7 @@ select 'a' || 'b' || 'c';
 
 -- Check if catalyst combine nested `Concat`s
 EXPLAIN EXTENDED SELECT (col1 || col2 || col3 || col4) col
-FROM (SELECT id col1, id col2, id col3, id col4 FROM range(10)) t;
+FROM (SELECT id col1, id col2, id col3, id col4 FROM range(10));
 
 -- replace function
 select replace('abc', 'b', '123');

sql/core/src/test/resources/sql-tests/inputs/subquery/in-subquery/in-set-operations.sql

@@ -394,7 +394,7 @@ FROM   (SELECT *
                              FROM   t1)) t4
         WHERE  t4.t2b IN (SELECT Min(t3b)
                           FROM   t3
-                          WHERE  t4.t2a = t3a)) T;
+                          WHERE  t4.t2a = t3a));
 
 -- UNION, UNION ALL, UNION DISTINCT, INTERSECT and EXCEPT for NOT IN
 -- TC 01.12

sql/core/src/test/resources/sql-tests/inputs/subquery/negative-cases/invalid-correlation.sql

@@ -23,7 +23,7 @@ AND    t2b = (SELECT max(avg)
               FROM   (SELECT   t2b, avg(t2b) avg
                       FROM     t2
                       WHERE    t2a = t1.t1b
-                     ) T
+                     )
              )
 ;
 

sql/core/src/test/resources/sql-tests/inputs/subquery/scalar-subquery/scalar-subquery-predicate.sql

@@ -19,7 +19,7 @@ AND    c.cv = (SELECT max(avg)
                FROM   (SELECT   c1.cv, avg(c1.cv) avg
                        FROM     c c1
                        WHERE    c1.ck = p.pk
-                       GROUP BY c1.cv) T);
+                       GROUP BY c1.cv));
 
 create temporary view t1 as select * from values
   ('val1a', 6S, 8, 10L, float(15.0), 20D, 20E2, timestamp '2014-04-04 00:00:00.000', date '2014-04-04'),

sql/core/src/test/resources/sql-tests/inputs/union.sql

@@ -5,15 +5,15 @@ CREATE OR REPLACE TEMPORARY VIEW t2 AS VALUES (1.0, 1), (2.0, 4) tbl(c1, c2);
 SELECT *
 FROM   (SELECT * FROM t1
         UNION ALL
-        SELECT * FROM t1) T;
+        SELECT * FROM t1);
 
 -- Type Coerced Union
 SELECT *
 FROM   (SELECT * FROM t1
         UNION ALL
         SELECT * FROM t2
         UNION ALL
-        SELECT * FROM t2) T;
+        SELECT * FROM t2);
 
 -- Regression test for SPARK-18622
 SELECT a

sql/core/src/test/resources/sql-tests/results/columnresolution-negative.sql.out

@@ -72,7 +72,7 @@ SELECT i1 FROM t1, mydb1.t1
 struct<>
 -- !query 8 output
 org.apache.spark.sql.AnalysisException
-Reference 'i1' is ambiguous, could be: i1#x, i1#x.; line 1 pos 7
+Reference 'i1' is ambiguous, could be: t1.i1, t1.i1.; line 1 pos 7
 
 
 -- !query 9
@@ -81,7 +81,7 @@ SELECT t1.i1 FROM t1, mydb1.t1
 struct<>
 -- !query 9 output
 org.apache.spark.sql.AnalysisException
-Reference 't1.i1' is ambiguous, could be: i1#x, i1#x.; line 1 pos 7
+Reference 't1.i1' is ambiguous, could be: t1.i1, t1.i1.; line 1 pos 7
 
 
 -- !query 10
@@ -99,7 +99,7 @@ SELECT i1 FROM t1, mydb2.t1
 struct<>
 -- !query 11 output
 org.apache.spark.sql.AnalysisException
-Reference 'i1' is ambiguous, could be: i1#x, i1#x.; line 1 pos 7
+Reference 'i1' is ambiguous, could be: t1.i1, t1.i1.; line 1 pos 7
 
 
 -- !query 12
@@ -108,7 +108,7 @@ SELECT t1.i1 FROM t1, mydb2.t1
 struct<>
 -- !query 12 output
 org.apache.spark.sql.AnalysisException
-Reference 't1.i1' is ambiguous, could be: i1#x, i1#x.; line 1 pos 7
+Reference 't1.i1' is ambiguous, could be: t1.i1, t1.i1.; line 1 pos 7
 
 
 -- !query 13
@@ -125,7 +125,7 @@ SELECT i1 FROM t1, mydb1.t1
 struct<>
 -- !query 14 output
 org.apache.spark.sql.AnalysisException
-Reference 'i1' is ambiguous, could be: i1#x, i1#x.; line 1 pos 7
+Reference 'i1' is ambiguous, could be: t1.i1, t1.i1.; line 1 pos 7
 
 
 -- !query 15
@@ -134,7 +134,7 @@ SELECT t1.i1 FROM t1, mydb1.t1
 struct<>
 -- !query 15 output
 org.apache.spark.sql.AnalysisException
-Reference 't1.i1' is ambiguous, could be: i1#x, i1#x.; line 1 pos 7
+Reference 't1.i1' is ambiguous, could be: t1.i1, t1.i1.; line 1 pos 7
 
 
 -- !query 16
@@ -143,7 +143,7 @@ SELECT i1 FROM t1, mydb2.t1
 struct<>
 -- !query 16 output
 org.apache.spark.sql.AnalysisException
-Reference 'i1' is ambiguous, could be: i1#x, i1#x.; line 1 pos 7
+Reference 'i1' is ambiguous, could be: t1.i1, t1.i1.; line 1 pos 7
 
 
 -- !query 17
@@ -152,7 +152,7 @@ SELECT t1.i1 FROM t1, mydb2.t1
 struct<>
 -- !query 17 output
 org.apache.spark.sql.AnalysisException
-Reference 't1.i1' is ambiguous, could be: i1#x, i1#x.; line 1 pos 7
+Reference 't1.i1' is ambiguous, could be: t1.i1, t1.i1.; line 1 pos 7
 
 
 -- !query 18

sql/core/src/test/resources/sql-tests/results/group-by.sql.out

@@ -134,7 +134,7 @@ struct<skewness(CAST(a AS DOUBLE)):double,kurtosis(CAST(a AS DOUBLE)):double,min
 
 
 -- !query 14
-SELECT COUNT(DISTINCT b), COUNT(DISTINCT b, c) FROM (SELECT 1 AS a, 2 AS b, 3 AS c) t GROUP BY a
+SELECT COUNT(DISTINCT b), COUNT(DISTINCT b, c) FROM (SELECT 1 AS a, 2 AS b, 3 AS c) GROUP BY a
 -- !query 14 schema
 struct<count(DISTINCT b):bigint,count(DISTINCT b, c):bigint>
 -- !query 14 output

sql/core/src/test/resources/sql-tests/results/limit.sql.out

@@ -93,7 +93,7 @@ The limit expression must be integer type, but got string;
 
 
 -- !query 10
-SELECT * FROM (SELECT * FROM range(10) LIMIT 5) t WHERE id > 3
+SELECT * FROM (SELECT * FROM range(10) LIMIT 5) WHERE id > 3
 -- !query 10 schema
 struct<id:bigint>
 -- !query 10 output

sql/core/src/test/resources/sql-tests/results/string-functions.sql.out

@@ -30,20 +30,20 @@ abc
 
 -- !query 3
 EXPLAIN EXTENDED SELECT (col1 || col2 || col3 || col4) col
-FROM (SELECT id col1, id col2, id col3, id col4 FROM range(10)) t
+FROM (SELECT id col1, id col2, id col3, id col4 FROM range(10))
 -- !query 3 schema
 struct<plan:string>
 -- !query 3 output
 == Parsed Logical Plan ==
 'Project [concat(concat(concat('col1, 'col2), 'col3), 'col4) AS col#x]
-+- 'SubqueryAlias t
++- 'SubqueryAlias _auto_generated_subquery_name
    +- 'Project ['id AS col1#x, 'id AS col2#x, 'id AS col3#x, 'id AS col4#x]
       +- 'UnresolvedTableValuedFunction range, [10]
 
 == Analyzed Logical Plan ==
 col: string
 Project [concat(concat(concat(cast(col1#xL as string), cast(col2#xL as string)), cast(col3#xL as string)), cast(col4#xL as string)) AS col#x]
-+- SubqueryAlias t
++- SubqueryAlias _auto_generated_subquery_name
    +- Project [id#xL AS col1#xL, id#xL AS col2#xL, id#xL AS col3#xL, id#xL AS col4#xL]
       +- Range (0, 10, step=1, splits=None)
 

sql/core/src/test/resources/sql-tests/results/subquery/in-subquery/in-set-operations.sql.out

@@ -496,7 +496,7 @@ FROM   (SELECT *
                              FROM   t1)) t4
         WHERE  t4.t2b IN (SELECT Min(t3b)
                           FROM   t3
-                          WHERE  t4.t2a = t3a)) T
+                          WHERE  t4.t2a = t3a))
 -- !query 13 schema
 struct<t2a:string,t2b:smallint,t2c:int,t2d:bigint,t2e:float,t2f:double,t2g:decimal(2,-2),t2h:timestamp,t2i:date>
 -- !query 13 output

sql/core/src/test/resources/sql-tests/results/subquery/negative-cases/invalid-correlation.sql.out

@@ -40,7 +40,7 @@ AND    t2b = (SELECT max(avg)
               FROM   (SELECT   t2b, avg(t2b) avg
                       FROM     t2
                       WHERE    t2a = t1.t1b
-                     ) T
+                     )
              )
 -- !query 3 schema
 struct<>

sql/core/src/test/resources/sql-tests/results/subquery/scalar-subquery/scalar-subquery-predicate.sql.out

@@ -39,7 +39,7 @@ AND    c.cv = (SELECT max(avg)
                FROM   (SELECT   c1.cv, avg(c1.cv) avg
                        FROM     c c1
                        WHERE    c1.ck = p.pk
-                       GROUP BY c1.cv) T)
+                       GROUP BY c1.cv))
 -- !query 3 schema
 struct<pk:int,cv:int>
 -- !query 3 output

sql/core/src/test/resources/sql-tests/results/subquery/subquery-in-from.sql.out

@@ -37,26 +37,14 @@ struct<key:int,value:string>
 -- !query 4
 SELECT * FROM (SELECT * FROM testData) WHERE key = 1
 -- !query 4 schema
-struct<>
+struct<key:int,value:string>
 -- !query 4 output
-org.apache.spark.sql.catalyst.parser.ParseException
-
-The unaliased subqueries in the FROM clause are not supported.(line 1, pos 14)
-
-== SQL ==
-SELECT * FROM (SELECT * FROM testData) WHERE key = 1
---------------^^^
+1	1
 
 
 -- !query 5
 FROM (SELECT * FROM testData WHERE key = 1) SELECT *
 -- !query 5 schema
-struct<>
+struct<key:int,value:string>
 -- !query 5 output
-org.apache.spark.sql.catalyst.parser.ParseException
-
-The unaliased subqueries in the FROM clause are not supported.(line 1, pos 5)
-
-== SQL ==
-FROM (SELECT * FROM testData WHERE key = 1) SELECT *
------^^^
+1	1

sql/core/src/test/resources/sql-tests/results/union.sql.out

@@ -22,7 +22,7 @@ struct<>
 SELECT *
 FROM   (SELECT * FROM t1
         UNION ALL
-        SELECT * FROM t1) T
+        SELECT * FROM t1)
 -- !query 2 schema
 struct<c1:int,c2:string>
 -- !query 2 output
@@ -38,7 +38,7 @@ FROM   (SELECT * FROM t1
         UNION ALL
         SELECT * FROM t2
         UNION ALL
-        SELECT * FROM t2) T
+        SELECT * FROM t2)
 -- !query 3 schema
 struct<c1:decimal(11,1),c2:string>
 -- !query 3 output

sql/core/src/test/scala/org/apache/spark/sql/CachedTableSuite.scala

@@ -631,13 +631,13 @@ class CachedTableSuite extends QueryTest with SQLTestUtils with SharedSQLContext
       val ds2 =
         sql(
           """
-            |SELECT * FROM (SELECT max(c1) as c1 FROM t1 GROUP BY c1) tt
+            |SELECT * FROM (SELECT c1, max(c1) FROM t1 GROUP BY c1)
             |WHERE
-            |tt.c1 = (SELECT max(c1) FROM t2 GROUP BY c1)
+            |c1 = (SELECT max(c1) FROM t2 GROUP BY c1)
             |OR
             |EXISTS (SELECT c1 FROM t3)
             |OR
-            |tt.c1 IN (SELECT c1 FROM t4)
+            |c1 IN (SELECT c1 FROM t4)
           """.stripMargin)
       assert(getNumInMemoryRelations(ds2) == 4)
     }
@@ -788,25 +788,25 @@ class CachedTableSuite extends QueryTest with SQLTestUtils with SharedSQLContext
       // Scalar subquery and predicate subquery
       sql(
         """
-          |SELECT * FROM (SELECT max(c1) as c1 FROM t1 GROUP BY c1) tt
+          |SELECT * FROM (SELECT c1, max(c1) as c1 FROM t1 GROUP BY c1)
           |WHERE
-          |tt.c1 = (SELECT max(c1) FROM t2 GROUP BY c1)
+          |c1 = (SELECT max(c1) FROM t2 GROUP BY c1)
           |OR
           |EXISTS (SELECT c1 FROM t3)
           |OR
-          |tt.c1 IN (SELECT c1 FROM t4)
+          |c1 IN (SELECT c1 FROM t4)
         """.stripMargin).cache()
 
       val cachedDs2 =
         sql(
           """
-            |SELECT * FROM (SELECT max(c1) as c1 FROM t1 GROUP BY c1) tt
+            |SELECT * FROM (SELECT c1, max(c1) as c1 FROM t1 GROUP BY c1)
             |WHERE
-            |tt.c1 = (SELECT max(c1) FROM t2 GROUP BY c1)
+            |c1 = (SELECT max(c1) FROM t2 GROUP BY c1)
             |OR
             |EXISTS (SELECT c1 FROM t3)
             |OR
-            |tt.c1 IN (SELECT c1 FROM t4)
+            |c1 IN (SELECT c1 FROM t4)
           """.stripMargin)
       assert(getNumInMemoryRelations(cachedDs2) == 1)
     }

sql/core/src/test/scala/org/apache/spark/sql/SQLQuerySuite.scala

@@ -2638,4 +2638,17 @@ class SQLQuerySuite extends QueryTest with SharedSQLContext {
       }
     }
   }
+
+  test("SPARK-21335: support un-aliased subquery") {
+    withTempView("v") {
+      Seq(1 -> "a").toDF("i", "j").createOrReplaceTempView("v")
+      checkAnswer(sql("SELECT i from (SELECT i FROM v)"), Row(1))
+
+      val e = intercept[AnalysisException](sql("SELECT v.i from (SELECT i FROM v)"))
+      assert(e.message ==
+        "cannot resolve '`v.i`' given input columns: [_auto_generated_subquery_name.i]")
+
+      checkAnswer(sql("SELECT _auto_generated_subquery_name.i from (SELECT i FROM v)"), Row(1))
+    }
+  }
 }