Github user marmbrus commented on a diff in the pull request:
https://github.com/apache/spark/pull/1325#discussion_r14633343
--- 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'm not sure what problem you are describing here. This rule takes a query
that is `attr LIKE 'something%' and turns it into the much faster
`attr.startsWith('something')`. Can you describe a case where that is not safe?
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