Github user marmbrus commented on a diff in the pull request: https://github.com/apache/spark/pull/1325#discussion_r14633377 --- Diff: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/Optimizer.scala --- @@ -112,6 +113,23 @@ 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 + val endsWith = "%([^_%]+)".r + val contains = "%([^_%]+)%".r + + def apply(plan: LogicalPlan): LogicalPlan = plan transformAllExpressions { + case Like(l, Literal(startsWith(pattern), StringType)) => StartsWith(l, Literal(pattern)) --- End diff -- I'll also note that this is not meant to be exaustive, but only cover some common cases that we can speed up 10x Hive does the same thing: https://github.com/apache/hive/blob/590c37f075def63e8507f2bfca820308b40e78b3/ql/src/java/org/apache/hadoop/hive/ql/exec/vector/expressions/FilterStringColLikeStringScalar.java#L64
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