Start of new ANTLR4 based parser.

Very simple tests pass.

pglablib/PgsqlParser.g4

@@ -0,0 +1,101 @@
+// Define a grammar called postgresql
+parser grammar PgsqlParser;
+
+options {
+	tokenVocab = PgsqlLexer;
+}
+
+@parser::preinclude {
+#include "sqlast/sqlast.h"
+}
+
+@parser::includes {
+}
+
+@parser::members {
+}
+
+main returns [std::unique_ptr<sqlast::StatementList> program]
+    : statement_list { $program = std::move($statement_list.result); }
+    ;
+
+statement_list returns [std::unique_ptr<sqlast::StatementList> result]
+    : { $result = std::make_unique<sqlast::StatementList>(); }
+      (statement SemiColon  { $result->Add(std::move($statement.result)); } | empty_statement)* 
+      (statement SemiColon? { $result->Add(std::move($statement.result)); } | empty_statement )
+    ;
+
+statement returns [std::unique_ptr<sqlast::Statement> result]
+    : select_stmt { $result = std::move($select_stmt.result); }
+    ;
+
+empty_statement
+    : SemiColon
+    ;
+
+select_stmt returns [std::unique_ptr<sqlast::SelectStatement> result]
+    : Select select_list 
+        { 
+            $result = std::make_unique<sqlast::SelectStatement>(); 
+            $result->SetSelectList(std::move($select_list.result));
+        }
+       (From from_item (Comma from_item)* )? 
+       (Where condition)? 
+       (Group By group_by)? 
+       (Order By order_by)? 
+       (Having having)?
+    ;
+
+from_item
+    : Ident Dot Ident from_alias?
+    | Ident from_alias?
+    | OpenParen select_stmt CloseParen from_alias
+    ;
+
+from_alias
+    : As? Ident (OpenParen Ident (Comma Ident)* CloseParen)?
+    ;
+
+condition
+    : expr
+    ;
+    
+group_by
+    :
+    ;
+    
+order_by
+    :
+    ;
+    
+having
+    :
+    ;
+    
+
+select_list returns [std::unique_ptr<sqlast::SelectList> result]
+    : select_item  
+        { 
+            $result = std::make_unique<sqlast::SelectList>(); 
+            $result->Add(std::move($select_item.result)); 
+        }
+        (Comma select_item)* { $result->Add(std::move($select_item.result)); }
+    | 
+    ;
+
+select_item returns [std::unique_ptr<sqlast::SelectItem> result]
+    : expr { $result = std::make_unique<sqlast::SelectItem>(std::move($expr.result)); }
+        (As? Ident { $result->SetAlias($Ident.text); })?
+    ;
+
+expr returns [std::unique_ptr<sqlast::Expression> result]
+    : expr Dot Ident
+    | Ident
+    | value { $result = std::move($value.result); }
+    ;
+
+value returns [std::unique_ptr<sqlast::Literal> result]
+    : IntegerLiteral
+    | StringLiteral { $result = std::make_unique<sqlast::StringLiteral>($StringLiteral.text); }
+    ;
+