oracle sql parser support keep

src/main/java/com/alibaba/druid/sql/ast/SQLKeep.java

@@ -0,0 +1,42 @@
+package com.alibaba.druid.sql.ast;
+
+import com.alibaba.druid.sql.visitor.SQLASTVisitor;
+
+public class SQLKeep extends SQLObjectImpl {
+
+    protected DenseRank  denseRank;
+
+    protected SQLOrderBy orderBy;
+
+    @Override
+    protected void accept0(SQLASTVisitor visitor) {
+        if (visitor.visit(this)) {
+            acceptChild(visitor, this.orderBy);
+        }
+        visitor.endVisit(this);
+    }
+
+    public DenseRank getDenseRank() {
+        return denseRank;
+    }
+
+    public void setDenseRank(DenseRank denseRank) {
+        this.denseRank = denseRank;
+    }
+
+    public SQLOrderBy getOrderBy() {
+        return orderBy;
+    }
+
+    public void setOrderBy(SQLOrderBy orderBy) {
+        if (orderBy != null) {
+            orderBy.setParent(this);
+        }
+        this.orderBy = orderBy;
+    }
+
+    public static enum DenseRank {
+                                  FIRST, //
+                                  LAST
+    }
+}