improve sql parser

src/main/java/com/alibaba/druid/sql/visitor/SQLEvalVisitorUtils.java

@@ -1239,6 +1239,14 @@ public class SQLEvalVisitorUtils {
                 return castToLong(list.get(0));
             }
         }
+        
+        if (val instanceof Boolean) {
+            if (((Boolean) val).booleanValue()) {
+                return 1l;
+            } else {
+                return 0l;
+            }
+        }
 
         return ((Number) val).longValue();
     }
@@ -1431,6 +1439,10 @@ public class SQLEvalVisitorUtils {
             return null;
         }
         
+        if(a == EVAL_VALUE_NULL || b == EVAL_VALUE_NULL) {
+            return null;
+        }
+        
         if (a instanceof String) {
             a = castToNumber((String) a);
         }

src/main/java/com/alibaba/druid/sql/visitor/functions/Char.java

@@ -42,8 +42,11 @@ public class Char implements Function {
                 int charCode = ((Number) paramValue).intValue();
                 buf.append((char) charCode);
             } else if (paramValue instanceof String) {
-                int charCode = new BigDecimal((String)paramValue).intValue();
-                buf.append((char) charCode);
+                try {
+                    int charCode = new BigDecimal((String) paramValue).intValue();
+                    buf.append((char) charCode);
+                } catch (NumberFormatException e) {
+                }
             } else {
                 return SQLEvalVisitor.EVAL_ERROR;
             }