implemented postgres table exists

backends/postgres/src/postgres_connection.cpp

@@ -134,7 +134,13 @@ sql::record postgres_connection::describe(const std::string &table)
 
 bool postgres_connection::exists(const std::string &table_name)
 {
-  return false;
+  std::string stmt("SELECT 1 FROM information_schema.tables WHERE table_schema = 'public' AND table_name = '" + table_name + "'");
+
+  PGresult *res = PQexec(conn_, stmt.c_str());
+
+  throw_postgres_error(res, conn_, "postgres", stmt);
+
+  return sql::to_long_long(PQcmdTuples(res)) == 1;
 }
 
 }