2 files changed, 55 insertions, 20 deletions
diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/regexpExpressions.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/regexpExpressions.scala
index 49b7797113..a36da8e94b 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/regexpExpressions.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/regexpExpressions.scala
@@ -69,7 +69,30 @@ abstract class StringRegexExpression extends BinaryExpression
  * Simple RegEx pattern matching function
  */
 @ExpressionDescription(
-  usage = "str _FUNC_ pattern - Returns true if `str` matches `pattern`, or false otherwise.")
+  usage = "str _FUNC_ pattern - Returns true if str matches pattern, " +
+    "null if any arguments are null, false otherwise.",
+  extended = """
+    Arguments:
+      str - a string expression
+      pattern - a string expression. The pattern is a string which is matched literally, with
+        exception to the following special symbols:
+
+          _ matches any one character in the input (similar to . in posix regular expressions)
+
+          % matches zero ore more characters in the input (similar to .* in posix regular
+          expressions)
+
+        The escape character is '\'. If an escape character precedes a special symbol or another
+        escape character, the following character is matched literally. It is invalid to escape
+        any other character.
+
+    Examples:
+      > SELECT '%SystemDrive%\Users\John' _FUNC_ '\%SystemDrive\%\\Users%'
+      true
+
+    See also:
+      Use RLIKE to match with standard regular expressions.
+""")
 case class Like(left: Expression, right: Expression) extends StringRegexExpression {
 
   override def escape(v: String): String = StringUtils.escapeLikeRegex(v)
diff --git a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/StringUtils.scala b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/StringUtils.scala
index cde8bd5b96..ca22ea2420 100644
--- a/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/StringUtils.scala
+++ b/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/util/StringUtils.scala
@@ -19,32 +19,44 @@ package org.apache.spark.sql.catalyst.util
 
 import java.util.regex.{Pattern, PatternSyntaxException}
 
+import org.apache.spark.sql.AnalysisException
 import org.apache.spark.unsafe.types.UTF8String
 
 object StringUtils {
 
-  // replace the _ with .{1} exactly match 1 time of any character
-  // replace the % with .*, match 0 or more times with any character
-  def escapeLikeRegex(v: String): String = {
-    if (!v.isEmpty) {
-      "(?s)" + (' ' +: v.init).zip(v).flatMap {
-        case (prev, '\\') => ""
-        case ('\\', c) =>
-          c match {
-            case '_' => "_"
-            case '%' => "%"
-            case _ => Pattern.quote("\\" + c)
-          }
-        case (prev, c) =>
+  /**
+   * Validate and convert SQL 'like' pattern to a Java regular expression.
+   *
+   * Underscores (_) are converted to '.' and percent signs (%) are converted to '.*', other
+   * characters are quoted literally. Escaping is done according to the rules specified in
+   * [[org.apache.spark.sql.catalyst.expressions.Like]] usage documentation. An invalid pattern will
+   * throw an [[AnalysisException]].
+   *
+   * @param pattern the SQL pattern to convert
+   * @return the equivalent Java regular expression of the pattern
+   */
+  def escapeLikeRegex(pattern: String): String = {
+    val in = pattern.toIterator
+    val out = new StringBuilder()
+
+    def fail(message: String) = throw new AnalysisException(
+      s"the pattern '$pattern' is invalid, $message")
+
+    while (in.hasNext) {
+      in.next match {
+        case '\\' if in.hasNext =>
+          val c = in.next
           c match {
-            case '_' => "."
-            case '%' => ".*"
-            case _ => Pattern.quote(Character.toString(c))
+            case '_' | '%' | '\\' => out ++= Pattern.quote(Character.toString(c))
+            case _ => fail(s"the escape character is not allowed to precede '$c'")
           }
-      }.mkString
-    } else {
-      v
+        case '\\' => fail("it is not allowed to end with the escape character")
+        case '_' => out ++= "."
+        case '%' => out ++= ".*"
+        case c => out ++= Pattern.quote(Character.toString(c))
+      }
     }
+    "(?s)" + out.result() // (?s) enables dotall mode, causing "." to match new lines
   }
 
   private[this] val trueStrings = Set("t", "true", "y", "yes", "1").map(UTF8String.fromString)