Start of new ANTLR4 based parser.

Very simple tests pass.

pglablib/sqlast/SelectItem.h

@@ -0,0 +1,25 @@
+#pragma once
+
+#include "Node.h"
+#include <memory>
+#include <string>
+
+namespace sqlast {
+
+class Expression;
+
+class SelectItem : public Node
+{
+public:
+    explicit SelectItem(std::unique_ptr<sqlast::Expression> expr);
+
+    Expression& GetExpression() { return *expression; }
+
+    void SetAlias(const std::string &alias);
+    std::string GetAlias() const { return alias; }
+private:
+    std::unique_ptr<Expression> expression;
+    std::string alias;
+};
+
+}