diff --git a/src/main/java/com/alibaba/druid/sql/visitor/SQLEvalVisitorUtils.java b/src/main/java/com/alibaba/druid/sql/visitor/SQLEvalVisitorUtils.java
index d602f7df43..31a86b2c52 100644
--- a/src/main/java/com/alibaba/druid/sql/visitor/SQLEvalVisitorUtils.java
+++ b/src/main/java/com/alibaba/druid/sql/visitor/SQLEvalVisitorUtils.java
@@ -931,7 +931,7 @@ public class SQLEvalVisitorUtils {
             return ((Number) val).intValue() == 1;
         }
 
-        throw new IllegalArgumentException();
+        throw new IllegalArgumentException(val.getClass() + " not supported.");
     }
 
     public static String castToString(Object val) {
@@ -1165,7 +1165,7 @@ public class SQLEvalVisitorUtils {
             return castToByte(a) + castToByte(b);
         }
 
-        throw new IllegalArgumentException();
+        throw new IllegalArgumentException(a.getClass() + " and " + b.getClass() + " not supported.");
     }
 
     public static Object div(Object a, Object b) {
@@ -1197,7 +1197,7 @@ public class SQLEvalVisitorUtils {
             return castToByte(a) / castToByte(b);
         }
 
-        throw new IllegalArgumentException();
+        throw new IllegalArgumentException(a.getClass() + " and " + b.getClass() + " not supported.");
     }
 
     public static boolean gt(Object a, Object b) {
@@ -1209,6 +1209,10 @@ public class SQLEvalVisitorUtils {
             return true;
         }
 
+        if (a instanceof String || b instanceof String) {
+            return ((String) a).compareTo((String) b) > 0;
+        }
+
         if (a instanceof BigDecimal || b instanceof BigDecimal) {
             return castToDecimal(a).compareTo(castToDecimal(b)) > 0;
         }
@@ -1252,7 +1256,7 @@ public class SQLEvalVisitorUtils {
             return d1.compareTo(d2) > 0;
         }
 
-        throw new IllegalArgumentException();
+        throw new IllegalArgumentException(a.getClass() + " and " + b.getClass() + " not supported.");
     }
 
     public static boolean gteq(Object a, Object b) {
@@ -1272,6 +1276,10 @@ public class SQLEvalVisitorUtils {
             return false;
         }
 
+        if (a instanceof String || b instanceof String) {
+            return ((String) a).compareTo((String) b) < 0;
+        }
+
         if (a instanceof BigDecimal || b instanceof BigDecimal) {
             return castToDecimal(a).compareTo(castToDecimal(b)) < 0;
         }
@@ -1315,7 +1323,7 @@ public class SQLEvalVisitorUtils {
             return d1.compareTo(d2) < 0;
         }
 
-        throw new IllegalArgumentException();
+        throw new IllegalArgumentException(a.getClass() + " and " + b.getClass() + " not supported.");
     }
 
     public static boolean lteq(Object a, Object b) {
@@ -1339,6 +1347,10 @@ public class SQLEvalVisitorUtils {
             return true;
         }
 
+        if (a instanceof String || b instanceof String) {
+            return castToString(a).equals(castToString(b));
+        }
+
         if (a instanceof BigDecimal || b instanceof BigDecimal) {
             return castToDecimal(a).compareTo(castToDecimal(b)) == 0;
         }
@@ -1378,11 +1390,7 @@ public class SQLEvalVisitorUtils {
             return d1.equals(d2);
         }
 
-        if (a instanceof String || b instanceof String) {
-            return castToString(a).equals(castToString(b));
-        }
-
-        throw new IllegalArgumentException();
+        throw new IllegalArgumentException(a.getClass() + " and " + b.getClass() + " not supported.");
     }
 
     public static Object add(Object a, Object b) {
@@ -1430,7 +1438,7 @@ public class SQLEvalVisitorUtils {
             return castToString(a) + castToString(b);
         }
 
-        throw new IllegalArgumentException();
+        throw new IllegalArgumentException(a.getClass() + " and " + b.getClass() + " not supported.");
     }
 
     public static Object sub(Object a, Object b) {
@@ -1514,7 +1522,7 @@ public class SQLEvalVisitorUtils {
             return castToByte(a) * castToByte(b);
         }
 
-        throw new IllegalArgumentException();
+        throw new IllegalArgumentException(a.getClass() + " and " + b.getClass() + " not supported.");
     }
 
     public static boolean like(String input, String pattern) {
diff --git a/src/main/java/com/alibaba/druid/sql/visitor/functions/Substring.java b/src/main/java/com/alibaba/druid/sql/visitor/functions/Substring.java
index 4ade056894..9e11949825 100644
--- a/src/main/java/com/alibaba/druid/sql/visitor/functions/Substring.java
+++ b/src/main/java/com/alibaba/druid/sql/visitor/functions/Substring.java
@@ -51,7 +51,7 @@ public class Substring implements Function {
         if (paramSize == 2) {
 
             if (index < 0) {
-                int lastIndex = str.length() + index ;
+                int lastIndex = str.length() + index;
                 return str.substring(lastIndex);
             }
 
@@ -66,15 +66,18 @@ public class Substring implements Function {
         }
 
         int len = ((Number) param2Value).intValue();
-        
+
         String result;
         if (index < 0) {
-            int lastIndex = str.length() + index ;
+            int lastIndex = str.length() + index;
             result = str.substring(lastIndex);
         } else {
             result = str.substring(index - 1);
         }
-        
+
+        if (len > result.length()) {
+            return result;
+        }
         return result.substring(0, len);
     }
 }