Github user marmbrus commented on a diff in the pull request: https://github.com/apache/spark/pull/1325#discussion_r14639873 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala --- @@ -112,6 +113,26 @@ object ColumnPruning extends Rule[LogicalPlan] { } /** + * Simplifies LIKE expressions that do not need full regular expressions to evaluate the condition. + * For example, when the expression is just checking to see if a string starts with a given + * pattern. + */ +object LikeSimplification extends Rule[LogicalPlan] { + val startsWith = "([^_%]+)%".r --- End diff -- We are conservative in that case and the optimization won't apply (but we'll still give a correct answer). I'm happy to update the regex if you have a better one... (this one is taken from Hive... though AFICT they don't check for `\` at the end at all).
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