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Subject [GitHub] [spark] dbtsai commented on a change in pull request #29565: [SPARK-24994][SQL] Add UnwrapCastInBinaryComparison optimizer to simplify literal types
Date Tue, 01 Sep 2020 05:17:24 GMT

dbtsai commented on a change in pull request #29565:
URL: https://github.com/apache/spark/pull/29565#discussion_r480824929



##########
File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/UnwrapCastInBinaryComparison.scala
##########
@@ -0,0 +1,216 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.sql.catalyst.optimizer
+
+import org.apache.spark.sql.catalyst.expressions._
+import org.apache.spark.sql.catalyst.expressions.Literal.FalseLiteral
+import org.apache.spark.sql.catalyst.plans.logical.LogicalPlan
+import org.apache.spark.sql.catalyst.rules.Rule
+import org.apache.spark.sql.types._
+
+/**
+ * Unwrap casts in binary comparison operations with patterns like following:
+ *
+ * `BinaryComparison(Cast(fromExp, toType), Literal(value, toType))`
+ *   or
+ * `BinaryComparison(Literal(value, toType), Cast(fromExp, toType))`
+ *
+ * This rule optimizes expressions with the above pattern by either replacing the cast with
simpler
+ * constructs, or moving the cast from the expression side to the literal side, which enables
them
+ * to be optimized away later and pushed down to data sources.
+ *
+ * Currently this only handles cases where `fromType` (of `fromExp`) and `toType` are of
integral
+ * types (i.e., byte, short, int and long). The rule checks to see if the literal `value`
is
+ * within range `(min, max)`, where `min` and `max` are the minimum and maximum value of
+ * `fromType`, respectively. If this is true then it means we can safely cast `value` to
`fromType`
+ * and thus able to move the cast to the literal side.
+ *
+ * If the `value` is not within range `(min, max)`, the rule breaks the scenario into different
+ * cases and try to replace each with simpler constructs.
+ *
+ * if `value > max`, the cases are of following:
+ *  - `cast(fromExp, toType) > value` ==> if(isnull(fromExp), null, false)
+ *  - `cast(fromExp, toType) >= value` ==> if(isnull(fromExp), null, false)
+ *  - `cast(fromExp, toType) === value` ==> if(isnull(fromExp), null, false)
+ *  - `cast(fromExp, toType) <=> value` ==> false
+ *  - `cast(fromExp, toType) <= value` ==> if(isnull(fromExp), null, true)
+ *  - `cast(fromExp, toType) < value` ==> if(isnull(fromExp), null, true)
+ *
+ * if `value == max`, the cases are of following:
+ *  - `cast(fromExp, toType) > value` ==> if(isnull(fromExp), null, false)
+ *  - `cast(fromExp, toType) >= value` ==> fromExp == max
+ *  - `cast(fromExp, toType) === value` ==> fromExp == max
+ *  - `cast(fromExp, toType) <=> value` ==> fromExp == max
+ *  - `cast(fromExp, toType) <= value` ==> if(isnull(fromExp), null, true)
+ *  - `cast(fromExp, toType) < value` ==> fromExp =!= max
+ *
+ * Similarly for the cases when `value == min` and `value < min`.
+ *
+ * Further, the above `if(isnull(fromExp), null, false)` is represented using conjunction
+ * `and(isnull(fromExp), null)`, to enable further optimization and filter pushdown to data
sources.
+ * Similarly, `if(isnull(fromExp), null, true)` is represented with `or(isnotnull(fromExp),
null)`.
+ */
+object UnwrapCastInBinaryComparison extends Rule[LogicalPlan] {
+  override def apply(plan: LogicalPlan): LogicalPlan = plan transform {
+    case l: LogicalPlan =>
+      l transformExpressionsUp {
+        case e @ BinaryComparison(_, _) => unwrapCast(e)
+      }
+  }
+
+  private def unwrapCast(exp: Expression): Expression = exp match {
+    case BinaryComparison(Literal(_, _), Cast(_, _, _)) =>
+      // Not a canonical form. In this case we first canonicalize the expression by swapping
the
+      // literal and cast side, then process the result and swap the literal and cast again
to
+      // restore the original order.
+      def swap(e: Expression): Expression = e match {
+        case GreaterThan(left, right) => LessThan(right, left)
+        case GreaterThanOrEqual(left, right) => LessThanOrEqual(right, left)
+        case EqualTo(left, right) => EqualTo(right, left)
+        case EqualNullSafe(left, right) => EqualNullSafe(right, left)
+        case LessThanOrEqual(left, right) => GreaterThanOrEqual(right, left)
+        case LessThan(left, right) => GreaterThan(right, left)
+        case _ => e
+      }
+

Review comment:
       remove this empty line.




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