Two single or double quote escapes single or double quote when string is surrounded by same type of quote

common/src/main/java/org/opensearch/sql/common/utils/StringUtils.java

@@ -27,16 +27,54 @@ public static String unquote(String text, String mark) {
 
   /**
    * Unquote Identifier which has " or ' or ` as mark.
+   * Strings quoted by ' or " with two of these quotes appearing next to each other in the quote
+   * acts as an escape
+   * Example: 'Test''s' will result in 'Test's', similar with those single quotes being replaced
+   * with double.
    * @param text string
    * @return An unquoted string whose outer pair of (single/double/back-tick) quotes have been
    *     removed
    */
   public static String unquoteText(String text) {
-    if (isQuoted(text, "\"") || isQuoted(text, "'") || isQuoted(text, "`")) {
-      return text.substring(1, text.length() - 1);
+
+    if (text.length() < 2) {
+      return text;
+    }
+
+    char enclosingQuote;
+    char firstChar = text.charAt(0);
+    char lastChar = text.charAt(text.length() - 1);
+
+    if (firstChar == lastChar
+        && (firstChar == '\''
+        || firstChar == '"'
+        || firstChar == '`')) {
+      enclosingQuote = firstChar;
     } else {
       return text;
     }
+
+    if (enclosingQuote == '`') {
+      return text.substring(1, text.length() - 1);
+    }
+
+    char currentChar;
+    char nextChar;
+
+    StringBuilder textSB = new StringBuilder();
+
+    // Ignores first and last character as they are the quotes that should be removed
+    for (int chIndex = 1; chIndex < text.length() - 1; chIndex++) {
+      currentChar = text.charAt(chIndex);
+      nextChar = text.charAt(chIndex + 1);
+      if (currentChar == enclosingQuote
+          && nextChar == currentChar) {
+        chIndex++;
+      }
+      textSB.append(currentChar);
+    }
+
+    return textSB.toString();
   }
 
   /**

core/src/test/java/org/opensearch/sql/common/utils/StringUtilsTest.java

@@ -0,0 +1,48 @@
+package org.opensearch.sql.common.utils;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.opensearch.sql.common.utils.StringUtils.unquoteText;
+
+import org.junit.jupiter.api.Test;
+
+class StringUtilsTest {
+  @Test
+  void unquoteTest() {
+    assertEquals("test", unquoteText("test"));
+    assertEquals("test", unquoteText("'test'"));
+    assertEquals("test", unquoteText("`test`"));
+
+    assertEquals("test'", unquoteText("'test'''"));
+    assertEquals("test\"", unquoteText("\"test\"\"\""));
+
+    assertEquals("te``st", unquoteText("'te``st'"));
+    assertEquals("te``st", unquoteText("\"te``st\""));
+    assertEquals("te``st", unquoteText("`te``st`"));
+
+    assertEquals("te'st", unquoteText("'te''st'"));
+    assertEquals("te''st", unquoteText("\"te''st\""));
+    assertEquals("te''st", unquoteText("`te''st`"));
+
+    assertEquals("te\"\"st", unquoteText("'te\"\"st'"));
+    assertEquals("te\"st", unquoteText("\"te\"\"st\""));
+    assertEquals("te\"\"st", unquoteText("`te\"\"st`"));
+
+    assertEquals("''", unquoteText("''''''"));
+    assertEquals("\"\"", unquoteText("\"\"\"\"\"\""));
+    assertEquals("````", unquoteText("``````"));
+
+    assertEquals("test'", unquoteText("'test''"));
+
+    assertEquals("", unquoteText(""));
+    assertEquals("'", unquoteText("'"));
+    assertEquals("`", unquoteText("`"));
+    assertEquals("\"", unquoteText("\""));
+
+    assertEquals("hello'", unquoteText("'hello''"));
+    assertEquals("don't", unquoteText("'don't'"));
+    assertEquals("hello`", unquoteText("`hello``"));
+    assertEquals("don\"t", unquoteText("\"don\"t\""));
+
+  }
+
+}

integ-test/src/test/resources/correctness/expressions/literals.txt

@@ -8,4 +8,7 @@ true
 2147483647
 -2147483648
 2147483648
--2147483649
+-2147483649
+'im'
+'i''m'
+'i""m'