Github user cloud-fan commented on a diff in the pull request:

    https://github.com/apache/spark/pull/22702#discussion_r224655771
  
    --- Diff: 
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/expressions.scala
 ---
    @@ -276,15 +276,15 @@ 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
     
    -      case a And (b Or c) if Not(a).semanticEquals(b) => And(a, c)
    -      case a And (b Or c) if Not(a).semanticEquals(c) => And(a, b)
    -      case (a Or b) And c if a.semanticEquals(Not(c)) => And(b, c)
    -      case (a Or b) And c if b.semanticEquals(Not(c)) => And(a, c)
    -
    -      case a Or (b And c) if Not(a).semanticEquals(b) => Or(a, c)
    -      case a Or (b And c) if Not(a).semanticEquals(c) => Or(a, b)
    -      case (a And b) Or c if a.semanticEquals(Not(c)) => Or(b, c)
    -      case (a And b) Or c if b.semanticEquals(Not(c)) => Or(a, c)
    +      case a And (b Or c) if !a.nullable && Not(a).semanticEquals(b) => 
And(a, c)
    --- End diff --
    
    assuming a is null, then b is also null.
    If c is null: `a And (b Or c)` -> null, And(a, c) -> null
    If c is true: `a And (b Or c)` -> null, And(a, c) -> null
    if c is false: `a And (b Or c)` -> null, And(a, c) -> false
    
    So yes this is a bug, and we should rewrite it to `If(IsNull(a), a, And(a, 
c))`


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