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[SPARK-25714][SQL][followup] improve the comment inside BooleanSimplification rule #22711

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[SPARK-25714][SQL][followup] improve the comment inside BooleanSimplification rule #22711

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improve the comment inside BooleanSimplification rule
cloud-fan Oct 13, 2018
21dab84
address comments
cloud-fan Oct 13, 2018
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24 changes: 15 additions & 9 deletions sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -276,31 +276,37 @@ object BooleanSimplification extends Rule[LogicalPlan] with PredicateHelper {
case a And b if a.semanticEquals(b) => a
case a Or b if a.semanticEquals(b) => a

// The following optimization is applicable only when the operands are not nullable,
// The following optimizations are applicable only when the operands are not nullable,
// since the three-value logic of AND and OR are different in NULL handling.
// See the chart:
// +---------+---------+---------+---------+
// | p | q | p OR q | p AND q |
// | operand | operand | OR | AND |
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@cloud-fan cloud-fan Oct 13, 2018

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AND and OR is commutative, so we can reduce the entries in this table

// +---------+---------+---------+---------+
// | TRUE | TRUE | TRUE | TRUE |
// | TRUE | FALSE | TRUE | FALSE |
// | TRUE | UNKNOWN | TRUE | UNKNOWN |
// | FALSE | TRUE | TRUE | FALSE |
// | FALSE | FALSE | FALSE | FALSE |
// | FALSE | UNKNOWN | UNKNOWN | FALSE |
// | UNKNOWN | TRUE | TRUE | UNKNOWN |
// | UNKNOWN | FALSE | UNKNOWN | FALSE |
// | UNKNOWN | UNKNOWN | UNKNOWN | UNKNOWN |
// +---------+---------+---------+---------+

// (NULL And (NULL Or FALSE)) = NULL, but (NULL And FALSE) = FALSE. Thus, a can't be nullable.
case a And (b Or c) if !a.nullable && Not(a).semanticEquals(b) => And(a, c)
// (NULL And (FALSE Or NULL)) = NULL, but (NULL And FALSE) = FALSE. Thus, a can't be nullable.
case a And (b Or c) if !a.nullable && Not(a).semanticEquals(c) => And(a, b)
case (a Or b) And c if !a.nullable && a.semanticEquals(Not(c)) => And(b, c)
case (a Or b) And c if !b.nullable && b.semanticEquals(Not(c)) => And(a, c)
// ((NULL Or FALSE) And NULL) = NULL, but (FALSE And NULL) = FALSE. Thus, c can't be nullable.
case (a Or b) And c if !c.nullable && a.semanticEquals(Not(c)) => And(b, c)
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@cloud-fan cloud-fan Oct 13, 2018

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b.nullable and c.nullable are same, because a.semanticEquals(Not(c)).

// ((FALSE Or NULL) And NULL) = NULL, but (FALSE And NULL) = FALSE. Thus, c can't be nullable.
case (a Or b) And c if !c.nullable && b.semanticEquals(Not(c)) => And(a, c)

// (NULL Or (NULL And TRUE)) = NULL, but (NULL Or TRUE) = TRUE. Thus, a can't be nullable.
case a Or (b And c) if !a.nullable && Not(a).semanticEquals(b) => Or(a, c)
// (NULL Or (TRUE And NULL)) = NULL, but (NULL Or TRUE) = TRUE. Thus, a can't be nullable.
case a Or (b And c) if !a.nullable && Not(a).semanticEquals(c) => Or(a, b)
case (a And b) Or c if !a.nullable && a.semanticEquals(Not(c)) => Or(b, c)
case (a And b) Or c if !b.nullable && b.semanticEquals(Not(c)) => Or(a, c)
// ((NULL And TRUE) Or NULL) = NULL, but (TRUE Or NULL) = TRUE. Thus, c can't be nullable.
case (a And b) Or c if !c.nullable && a.semanticEquals(Not(c)) => Or(b, c)
// ((TRUE And NULL) Or NULL) = NULL, but (TRUE Or NULL) = TRUE. Thus, c can't be nullable.
case (a And b) Or c if !c.nullable && b.semanticEquals(Not(c)) => Or(a, c)

// Common factor elimination for conjunction
case and @ (left And right) =>
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