[GitHub] [spark] cloud-fan commented on a change in pull request #27507: [SPARK-24884][SQL] Support regexp function regexp_extract_all

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cloud-fan commented on a change in pull request #27507:
URL: https://github.com/apache/spark/pull/27507#discussion_r462993465



##########
File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/regexpExpressions.scala
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@@ -421,20 +423,59 @@ object RegExpExtract {
   }
 }
 
+abstract class RegExpExtractBase
+  extends TernaryExpression with ImplicitCastInputTypes with NullIntolerant {
+  def subject: Expression
+  def regexp: Expression
+  def idx: Expression
+
+  // last regex in string, we will update the pattern iff regexp value changed.
+  @transient private var lastRegex: UTF8String = _
+  // last regex pattern, we cache it for performance concern
+  @transient private var pattern: Pattern = _
+
+  override def inputTypes: Seq[AbstractDataType] = Seq(StringType, StringType, IntegerType)
+  override def children: Seq[Expression] = subject :: regexp :: idx :: Nil
+
+  protected def getLastMatcher(s: Any, p: Any): Matcher = {
+    if (!p.equals(lastRegex)) {
+      // regex value changed
+      lastRegex = p.asInstanceOf[UTF8String].clone()
+      pattern = Pattern.compile(lastRegex.toString)
+    }
+    pattern.matcher(s.toString)
+  }
+}
+
 /**
  * Extract a specific(idx) group identified by a Java regex.
  *
  * NOTE: this expression is not THREAD-SAFE, as it has some internal mutable status.
  */
 @ExpressionDescription(
-  usage = "_FUNC_(str, regexp[, idx]) - Extracts a group that matches `regexp`.",
+  usage = """
+    _FUNC_(str, regexp[, idx]) - Extract the first string in the `str` that match the `regexp`
+    expression and corresponding to the regex group index.
+  """,
   arguments = """
     Arguments:
       * str - a string expression.
-      * regexp - a string representing a regular expression.
-          The regex string should be a Java regular expression.
-      * idx - an integer expression that representing the group index. The group index should be
-          non-negative. If `idx` is not specified, the default group index value is 1.
+      * regexp - a string representing a regular expression. The regex string should be a
+          Java regular expression.
+
+          Since Spark 2.0, string literals (including regex patterns) are unescaped in our SQL
+          parser. For example, to match "\abc", a regular expression for `regexp` can be
+          "^\\abc$".
+
+          There is a SQL config 'spark.sql.parser.escapedStringLiterals' that can be used to
+          fallback to the Spark 1.6 behavior regarding string literal parsing. For example,
+          if the config is enabled, the `regexp` that can match "\abc" is "^\abc$".
+      * idx - an integer expression that representing the group index. The regex maybe contains
+          multiple groups. `idx` indicates which regex group to extract. The group index should
+          be non-negative. If `idx` is not specified, the default group index value is 1. The

Review comment:
       It's important to mention the start point. Seems the `idx` starts with 1 not 0?




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