How to convert time () * 1000 to string in Y-m-d H:i:s format by PHP

as mentioned, how does PHP convert time () * 1000 to a string in Y-m-d H:i:s format

Php
Jul.09,2021

<?php

date_default_timezone_set('Asia/Shanghai');

$dat = time()*1000;

echo date('Y-m-d H-i-s', $dat/1000);
echo "\n";
MySQL Query : SELECT * FROM `codeshelper`.`v9_news` WHERE status=99 AND catid='6' ORDER BY rand() LIMIT 5
MySQL Error : Disk full (/tmp/#sql-temptable-64f5-1b3e49d-2c40b.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
MySQL Errno : 1021
Message : Disk full (/tmp/#sql-temptable-64f5-1b3e49d-2c40b.MAI); waiting for someone to free some space... (errno: 28 "No space left on device")
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