Github user gatorsmile commented on a diff in the pull request:
https://github.com/apache/spark/pull/23139#discussion_r236157802
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/ReplaceNullWithFalseInPredicate.scala
---
@@ -0,0 +1,107 @@
+/*
+ * 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.{And, ArrayExists,
ArrayFilter, CaseWhen, Expression, If}
+import org.apache.spark.sql.catalyst.expressions.{LambdaFunction, Literal,
MapFilter, Or}
+import org.apache.spark.sql.catalyst.expressions.Literal.FalseLiteral
+import org.apache.spark.sql.catalyst.plans.logical.{Filter, Join,
LogicalPlan}
+import org.apache.spark.sql.catalyst.rules.Rule
+import org.apache.spark.sql.types.BooleanType
+
+
+/**
+ * A rule that replaces `Literal(null, BooleanType)` with `FalseLiteral`,
if possible, in the search
+ * condition of the WHERE/HAVING/ON(JOIN) clauses, which contain an
implicit Boolean operator
+ * "(search condition) = TRUE". The replacement is only valid when
`Literal(null, BooleanType)` is
+ * semantically equivalent to `FalseLiteral` when evaluating the whole
search condition.
+ *
+ * Please note that FALSE and NULL are not exchangeable in most cases,
when the search condition
+ * contains NOT and NULL-tolerant expressions. Thus, the rule is very
conservative and applicable
+ * in very limited cases.
+ *
+ * For example, `Filter(Literal(null, BooleanType))` is equal to
`Filter(FalseLiteral)`.
+ *
+ * Another example containing branches is `Filter(If(cond, FalseLiteral,
Literal(null, _)))`;
+ * this can be optimized to `Filter(If(cond, FalseLiteral,
FalseLiteral))`, and eventually
+ * `Filter(FalseLiteral)`.
+ *
+ * Moreover, this rule also transforms predicates in all [[If]]
expressions as well as branch
+ * conditions in all [[CaseWhen]] expressions, even if they are not part
of the search conditions.
+ *
+ * For example, `Project(If(And(cond, Literal(null)), Literal(1),
Literal(2)))` can be simplified
+ * into `Project(Literal(2))`.
+ */
+object ReplaceNullWithFalseInPredicate extends Rule[LogicalPlan] {
+
+ def apply(plan: LogicalPlan): LogicalPlan = plan transform {
+ case f @ Filter(cond, _) => f.copy(condition =
replaceNullWithFalse(cond))
+ case j @ Join(_, _, _, Some(cond)) => j.copy(condition =
Some(replaceNullWithFalse(cond)))
+ case p: LogicalPlan => p transformExpressions {
+ case i @ If(pred, _, _) => i.copy(predicate =
replaceNullWithFalse(pred))
+ case cw @ CaseWhen(branches, _) =>
+ val newBranches = branches.map { case (cond, value) =>
+ replaceNullWithFalse(cond) -> value
+ }
+ cw.copy(branches = newBranches)
+ case af @ ArrayFilter(_, lf @ LambdaFunction(func, _, _)) =>
+ val newLambda = lf.copy(function = replaceNullWithFalse(func))
+ af.copy(function = newLambda)
+ case ae @ ArrayExists(_, lf @ LambdaFunction(func, _, _)) =>
+ val newLambda = lf.copy(function = replaceNullWithFalse(func))
+ ae.copy(function = newLambda)
+ case mf @ MapFilter(_, lf @ LambdaFunction(func, _, _)) =>
+ val newLambda = lf.copy(function = replaceNullWithFalse(func))
+ mf.copy(function = newLambda)
+ }
+ }
+
+ /**
+ * Recursively traverse the Boolean-type expression to replace
+ * `Literal(null, BooleanType)` with `FalseLiteral`, if possible.
+ *
+ * Note that `transformExpressionsDown` can not be used here as we must
stop as soon as we hit
+ * an expression that is not [[CaseWhen]], [[If]], [[And]], [[Or]] or
+ * `Literal(null, BooleanType)`.
+ */
+ private def replaceNullWithFalse(e: Expression): Expression = {
+ if (e.dataType != BooleanType) {
--- End diff --
See this line
https://github.com/apache/spark/pull/23139/files/e41681096867cbc6d2556da83ce733092d6df841#diff-a1acb054bc8888376603ef510e6d0ee0
My major concern is we should not completely rely on the caller to ensure
the data type is Boolean. In the future, the new code changes might not
completely follow our current assumption.
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