[GitHub] [spark] viirya commented on a change in pull request #29565: [SPARK-24994][SQL] Add UnwrapCastInBinaryComparison optimizer to simplify literal types

[GitBox <gi...@apache.org>]

viirya commented on a change in pull request #29565:
URL: https://github.com/apache/spark/pull/29565#discussion_r486063074



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File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/UnwrapCastInBinaryComparison.scala
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@@ -0,0 +1,204 @@
+/*
+ * 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 (only if `fromExp` is deterministic)
+ *  - `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

Review comment:
       `fromExp <=> max`?
   
   For `cast(fromExp, toType) <=> value`, if `fromExp` is null, original binary expression evaluates to false. But `fromExp == max` evaluates to null, right?




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