Github user rxin commented on a diff in the pull request:
https://github.com/apache/spark/pull/1325#discussion_r14640036
--- 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 --
Actually this sounds good (it's just not a case to optimize for). Can we
add comment inline to explain that? i.e. "This doesn't match case like
"abcd\\%", but it doesn't affect correctness."
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