[SPARK-24128][SQL] Mention configuration option in implicit CROSS JOI…

…N error

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala

@@ -1182,12 +1182,14 @@ object CheckCartesianProducts extends Rule[LogicalPlan] with PredicateHelper {
       case j @ Join(left, right, Inner | LeftOuter | RightOuter | FullOuter, _)
         if isCartesianProduct(j) =>
           throw new AnalysisException(
-            s"""Detected cartesian product for ${j.joinType.sql} join between logical plans
+            s"""Detected implicit cartesian product for ${j.joinType.sql} join between logical plans
                |${left.treeString(false).trim}
                |and
                |${right.treeString(false).trim}
                |Join condition is missing or trivial.
-               |Use the CROSS JOIN syntax to allow cartesian products between these relations."""
+               |Either: use the CROSS JOIN syntax to allow cartesian products between these
+               |relations, or: enable implicit cartesian products by setting the configuration
+               |variable spark.sql.crossJoin.enabled=true"""
             .stripMargin)
     }
 }

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/optimizer/CheckCartesianProductsSuite.scala

@@ -56,7 +56,7 @@ class CheckCartesianProductsSuite extends PlanTest {
         val thrownException = the [AnalysisException] thrownBy {
           performCartesianProductCheck(joinType)
         }
-        assert(thrownException.message.contains("Detected cartesian product"))
+        assert(thrownException.message.contains("Detected implicit cartesian product"))
       }
     }
   }

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

@@ -239,7 +239,7 @@ class JoinSuite extends QueryTest with SharedSQLContext {
             Row(2, 2, 1, null) ::
             Row(2, 2, 2, 2) :: Nil)
       }
-      assert(e.getMessage.contains("Detected cartesian product for INNER join " +
+      assert(e.getMessage.contains("Detected implicit cartesian product for INNER join " +
         "between logical plans"))
     }
   }
@@ -611,7 +611,7 @@ class JoinSuite extends QueryTest with SharedSQLContext {
       val e = intercept[Exception] {
         checkAnswer(sql(query), Nil);
       }
-      assert(e.getMessage.contains("Detected cartesian product"))
+      assert(e.getMessage.contains("Detected implicit cartesian product"))
     }
 
     cartesianQueries.foreach(checkCartesianDetection)