diff --git a/src/main/java/com/alibaba/druid/sql/visitor/SQLASTOutputVisitor.java b/src/main/java/com/alibaba/druid/sql/visitor/SQLASTOutputVisitor.java
index 4c0781932e..39b0841064 100644
--- a/src/main/java/com/alibaba/druid/sql/visitor/SQLASTOutputVisitor.java
+++ b/src/main/java/com/alibaba/druid/sql/visitor/SQLASTOutputVisitor.java
@@ -1192,6 +1192,16 @@ public class SQLASTOutputVisitor extends SQLASTVisitorAdapter implements Printab
         return false;
     }
 
+    public boolean visit(NullConstraint x) {
+    	if (x.getName() != null) {
+    		print0(ucase ? "CONSTRAINT " : "constraint ");
+    		x.getName().accept(this);
+    		print(' ');
+    	}
+    	print0(ucase ? "NULL" : "null");
+    	return false;
+    }
+
     @Override
     public boolean visit(SQLUnionQuery x) {
         x.getLeft().accept(this);
diff --git a/src/main/java/com/alibaba/druid/sql/visitor/SQLASTVisitor.java b/src/main/java/com/alibaba/druid/sql/visitor/SQLASTVisitor.java
index 0f641957e7..61df27ff28 100644
--- a/src/main/java/com/alibaba/druid/sql/visitor/SQLASTVisitor.java
+++ b/src/main/java/com/alibaba/druid/sql/visitor/SQLASTVisitor.java
@@ -716,4 +716,9 @@ public interface SQLASTVisitor {
     boolean visit(SQLErrorLoggingClause x);
 
     void endVisit(SQLErrorLoggingClause x);
+
+    boolean visit(NullConstraint x);
+
+    void endVisit(NullConstraint x);
+
 }
diff --git a/src/main/java/com/alibaba/druid/sql/visitor/SQLASTVisitorAdapter.java b/src/main/java/com/alibaba/druid/sql/visitor/SQLASTVisitorAdapter.java
index fb20641240..182962c8df 100644
--- a/src/main/java/com/alibaba/druid/sql/visitor/SQLASTVisitorAdapter.java
+++ b/src/main/java/com/alibaba/druid/sql/visitor/SQLASTVisitorAdapter.java
@@ -1565,4 +1565,13 @@ public class SQLASTVisitorAdapter implements SQLASTVisitor {
     public void endVisit(SQLErrorLoggingClause x) {
 
     }
+
+    @Override
+    public boolean visit(NullConstraint x) {
+	return true;
+    }
+
+    @Override
+    public void endVisit(NullConstraint x) {
+    }
 }