void fromUnixtime(HplsqlParser.Expr_func_paramsContext ctx) {
    int cnt = BuiltinFunctions.getParamCount(ctx);
    if (cnt == 0) {
      evalNull();
      return;
    }
    Var value = evalPop(ctx.func_param(0).expr());
    if (value.type != Var.Type.BIGINT) {
      Var newVar = new Var(Var.Type.BIGINT);
      value = newVar.cast(value);
    }
    long epoch = value.longValue();
    String format = "yyyy-MM-dd HH:mm:ss";
    if (cnt > 1) {
      format = Utils.unquoteString(evalPop(ctx.func_param(1).expr()).toString());
    }
    DateTimeFormatter formatter = createDateTimeFormatter(format);
    evalString(formatter.format(new java.sql.Date(epoch * 1000).toLocalDate()));
  }
FROM_UNIXTIME() function (convert seconds since 1970-01-01 00:00:00 to timestamp)
hplsql/src/main/java/org/apache/hive/hplsql/functions/FunctionDatetime.java