[GitHub] [pinot] walterddr commented on a diff in pull request #8893: Optimize like to regexp conversion to do not include unnecessary ^.* and .*$

[GitBox <gi...@apache.org>]

walterddr commented on code in PR #8893:
URL: https://github.com/apache/pinot/pull/8893#discussion_r913887685


##########
pinot-common/src/main/java/org/apache/pinot/common/utils/RegexpPatternConverterUtils.java:
##########
@@ -33,7 +33,49 @@ private RegexpPatternConverterUtils() {
    * Converts a LIKE pattern into REGEXP_LIKE pattern.
    */
   public static String likeToRegexpLike(String likePattern) {
-    return "^" + escapeMetaCharacters(likePattern).replace('_', '.').replace("%", ".*") + "$";
+    int start = 0;
+    int end = likePattern.length();
+    String prefix = "^";
+    String suffix = "$";
+    switch (likePattern.length()) {
+      case 0:
+        return "^$";
+      case 1:
+        if (likePattern.charAt(0) == '%') {
+          return "^.*$";
+        }
+        break;
+      default:
+        if (likePattern.charAt(0) == '%') {

Review Comment:
   thanks for the explanation. it just seems ok to recursively prune out leading/trailing `%` e.g. instead of 
   `start = 1;` we can do start equal to first non `%` char. 



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