Updated Druid_SQL_AST (markdown)

Druid_SQL_AST.md

@@ -163,7 +163,8 @@ class SQLUnionQuery implements SQLSelectQuery {
 }
 ```
 
-## 2.5 SQLCreateTableStatement
+## 2.5. SQLCreateTableStatement
+建表语句包含了一系列方法，用于方便各种操作
 ```java
 public class SQLCreateTableStatement extends SQLStatementImpl implements SQLDDLStatement, SQLCreateStatement {
     SQLExprTableSource tableSource;
@@ -174,7 +175,10 @@ public class SQLCreateTableStatement extends SQLStatementImpl implements SQLDDLS
     public SQLColumnDefinition findColumn(String columName) {}
 
     // 忽略大小写的查找SQLCreateTableStatement中的column关联的索引
-    public SQLTableElement findIndex(String columnName);
+    public SQLTableElement findIndex(String columnName) {}
+
+    // 是否外键依赖另外一个表
+    public boolean isReferenced(String tableName) {}
 }
 ```