[SPARK-13789] Infer additional constraints from attribute equality

## What changes were proposed in this pull request?

This PR adds support for inferring an additional set of data constraints based on attribute equality. For e.g., if an operator has constraints of the form (`a = 5`, `a = b`), we can now automatically infer an additional constraint of the form `b = 5`

## How was this patch tested?

Tested that new constraints are properly inferred for filters (by adding a new test) and equi-joins (by modifying an existing test)

Author: Sameer Agarwal <sameer@databricks.com>

Closes #11618 from sameeragarwal/infer-isequal-constraints.

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/plans/QueryPlan.scala

@@ -32,6 +32,7 @@ abstract class QueryPlan[PlanType <: QueryPlan[PlanType]] extends TreeNode[PlanT
    */
   protected def getRelevantConstraints(constraints: Set[Expression]): Set[Expression] = {
     constraints
+      .union(inferAdditionalConstraints(constraints))
       .union(constructIsNotNullConstraints(constraints))
       .filter(constraint =>
         constraint.references.nonEmpty && constraint.references.subsetOf(outputSet))
@@ -63,6 +64,26 @@ abstract class QueryPlan[PlanType <: QueryPlan[PlanType]] extends TreeNode[PlanT
     }.foldLeft(Set.empty[Expression])(_ union _.toSet)
   }
 
+  /**
+   * Infers an additional set of constraints from a given set of equality constraints.
+   * For e.g., if an operator has constraints of the form (`a = 5`, `a = b`), this returns an
+   * additional constraint of the form `b = 5`
+   */
+  private def inferAdditionalConstraints(constraints: Set[Expression]): Set[Expression] = {
+    var inferredConstraints = Set.empty[Expression]
+    constraints.foreach {
+      case eq @ EqualTo(l: Attribute, r: Attribute) =>
+        inferredConstraints ++= (constraints - eq).map(_ transform {
+          case a: Attribute if a.semanticEquals(l) => r
+        })
+        inferredConstraints ++= (constraints - eq).map(_ transform {
+          case a: Attribute if a.semanticEquals(r) => l
+        })
+      case _ => // No inference
+    }
+    inferredConstraints -- constraints
+  }
+
   /**
    * An [[ExpressionSet]] that contains invariants about the rows output by this operator. For
    * example, if this set contains the expression `a = 2` then that expression is guaranteed to

sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/plans/ConstraintPropagationSuite.scala

@@ -158,6 +158,7 @@ class ConstraintPropagationSuite extends SparkFunSuite {
         tr2.resolveQuoted("d", caseInsensitiveResolution).get < 100,
         tr1.resolveQuoted("a", caseInsensitiveResolution).get ===
           tr2.resolveQuoted("a", caseInsensitiveResolution).get,
+        tr2.resolveQuoted("a", caseInsensitiveResolution).get > 10,
         IsNotNull(tr2.resolveQuoted("a", caseInsensitiveResolution).get),
         IsNotNull(tr1.resolveQuoted("a", caseInsensitiveResolution).get),
         IsNotNull(tr2.resolveQuoted("d", caseInsensitiveResolution).get))))
@@ -203,4 +204,17 @@ class ConstraintPropagationSuite extends SparkFunSuite {
       .join(tr2.where('d.attr < 100), FullOuter, Some("tr1.a".attr === "tr2.a".attr))
       .analyze.constraints.isEmpty)
   }
+
+  test("infer additional constraints in filters") {
+    val tr = LocalRelation('a.int, 'b.int, 'c.int)
+
+    verifyConstraints(tr
+      .where('a.attr > 10 && 'a.attr === 'b.attr)
+      .analyze.constraints,
+      ExpressionSet(Seq(resolveColumn(tr, "a") > 10,
+        resolveColumn(tr, "b") > 10,
+        resolveColumn(tr, "a") === resolveColumn(tr, "b"),
+        IsNotNull(resolveColumn(tr, "a")),
+        IsNotNull(resolveColumn(tr, "b")))))
+  }
 }