improved sql parser.

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

@@ -0,0 +1,39 @@
+package com.alibaba.druid.sql.ast;
+
+import com.alibaba.druid.sql.visitor.SQLASTVisitor;
+
+/**
+ * Created by wenshao on 29/05/2017.
+ */
+public class SQLArgument extends SQLObjectImpl {
+    private SQLParameter.ParameterType type;
+    private SQLExpr expr;
+
+    @Override
+    protected void accept0(SQLASTVisitor visitor) {
+        if (visitor.visit(this)) {
+            acceptChild(visitor, expr);
+        }
+
+        visitor.endVisit(this);
+    }
+
+    public SQLParameter.ParameterType getType() {
+        return type;
+    }
+
+    public SQLExpr getExpr() {
+        return expr;
+    }
+
+    public void setType(SQLParameter.ParameterType type) {
+        this.type = type;
+    }
+
+    public void setExpr(SQLExpr expr) {
+        if (expr != null) {
+            expr.setParent(this);
+        }
+        this.expr = expr;
+    }
+}