From 6ad7fa902ba12615d6b31136c5a83dd8d402a64d Mon Sep 17 00:00:00 2001
From: juicer <wgzhsd@gmail.com>
Date: Fri, 29 Jul 2016 18:33:22 +0800
Subject: [PATCH] =?UTF-8?q?=E4=BF=AE=E6=94=B9=E5=85=B3=E4=BA=8E=20NULL=20?=
 =?UTF-8?q?=E7=9A=84=E9=97=AE=E9=A2=98?=
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Oracle 中  原始sql  ：alter table aaa modify bbb null;
转换后成为：  ALTER TABLE  aaa  MODIFY ( bbb DEFAULT NULL );
原始Sql的语义改变了，改变了字段的default值
---
 .../alibaba/druid/sql/visitor/SQLASTOutputVisitor.java | 10 ++++++++++
 .../com/alibaba/druid/sql/visitor/SQLASTVisitor.java   |  5 +++++
 .../druid/sql/visitor/SQLASTVisitorAdapter.java        |  9 +++++++++
 3 files changed, 24 insertions(+)

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) {
+    }
 }