Editing Convert between date and unix timestamp

=== terms of time format ===
<div style="width:100%; min-height: .01%; overflow-x: auto;"> 
<table border="1" class="wikitable sortable nowrap">
<tr>
  <th> format \ date </th>
  <th> 1899/12/31 (1900/1/0)</th>
  <th> 1900/1/1</th>
  <th> 1970/1/1</th>
  <th> 2016/1/1 </th>
  <th> notes </th>
</tr>
<tr>
  <td> value of unix timestamp <br /> (the number of seconds since 1970/01/01<ref>[https://www.extendoffice.com/documents/excel/2473-excel-timestamp-to-date.html How to convert between date and Unix timestamp in Excel?]</ref>)</td>
  <td> -2209075200</td>
  <td> -2208988800</td>
  <td> 0</td>
  <td> 1451606400</td>
  <td> </td>
</tr>
<tr>
  <td> value of Excel [https://support.office.com/zh-tw/article/DATEVALUE-%E5%87%BD%E6%95%B8-df8b07d4-7761-4a93-bc33-b7471bbff252 DATEVALUE] function or LibreOffice [https://help.libreoffice.org/Calc/DATEVALUE/zh-TW DATEVALUE] function<br />  (Excel: number of days since 1898/12/31) </td>
  <td> 0</td>
  <td> 1</td>
  <td> 25569</td>
  <td> 42370</td>
  <td> 5 digit numbers after 1970/1/1 </td>
</tr>
</table>
</div>

{{exclaim}} [https://support.office.com/zh-tw/article/value-%E5%87%BD%E6%95%B8-257d0108-07dc-437d-ae1c-bc2d3953d8c2 VALUE()] function on Excel is  number of days since 1899/12/31. DATEVALUE of 1900/1/1 will return 1. [https://support.google.com/docs/answer/3094220?hl=en VALUE()] function on Google sheet is number of days since 1899/12/30 {{access | date=2019-05-22}}

== Convert between date and unix timestamp ==

Online tool
* {{Gd}} [https://www.unixtimestamp.com/index.php Unix Time Stamp - Epoch Converter]

<pre>
// timestamp: 1552521600
// Is equivalent to:
// 03/14/2019 @ 12:00am (UTC)
// 2019-03-14T00:00:00+00:00 in ISO 8601
// Thu, 14 Mar 2019 00:00:00 +0000 in RFC 822, 1036, 1123, 2822
// Thursday, 14-Mar-19 00:00:00 UTC in RFC 2822
// 2019-03-14T00:00:00+00:00 in RFC 3339
</pre>

=== PHP way: convert to date time from unix timestamp ===
Using the [https://www.php.net/manual/en/function.date.php date()] function & [https://www.php.net/manual/en/function.date-default-timezone-set.php date_default_timezone_set]
<pre>
date_default_timezone_set('UTC');
$timestamp = 0;
echo date('Y-m-d H:i:s', $timestamp) . PHP_EOL; // 1970-01-01 00:00:00

date_default_timezone_set("Europe/London");
$timestamp = 1552521600;
echo date('Y-m-d H:i:s', $timestamp) . PHP_EOL; // 2019-03-14 00:00:00

date_default_timezone_set("Asia/Taipei");
$timestamp = 1552521600;
echo date('Y-m-d H:i:s', $timestamp) . PHP_EOL; // 2019-03-14 08:00:00
</pre>

=== PHP way: convert to unix timestamp from date time ===
Using the [https://www.php.net/manual/en/function.strtotime.php strtotime()] function
<pre>
date_default_timezone_set("Europe/London");
echo strtotime('2019-03-14 00:00:00') . PHP_EOL; // 1552521600

date_default_timezone_set("Asia/Taipei");
echo strtotime('2019-03-14 08:00:00') . PHP_EOL; // 1552521600
</pre>

=== Excel way: convert to date from unix timestamp ===
* [https://errerrors.blogspot.com/2019/09/how-to-convert-between-date-and-unix-timestamp-in-excel.html 怎樣轉換 Excel 日期時間成 Unix 時間戳記 (unix timestamp)]
* [https://www.extendoffice.com/documents/excel/2473-excel-timestamp-to-date.html How to convert between date and Unix timestamp in Excel?]

timezone: UTC
<pre>
= (VALUE( date_time )-25569)*86400
</pre>

=== Excel way: convert to unix timestamp from date ===
input data (A2 cell): YYYY/MM/DD (e.g. {{CURRENTYEAR}}/{{CURRENTMONTH}}/{{CURRENTDAY2}} ) or YYYY/MM/DD HH:MM (e.g. {{CURRENTYEAR}}/{{CURRENTMONTH}}/{{CURRENTDAY2}} {{CURRENTTIME}}) {{kbd | key==(A2-DATE(1970,1,1))*86400}} <ref>[http://stackoverflow.com/questions/1703505/excel-date-to-unix-timestamp Excel date to Unix timestamp - Stack Overflow]</ref>

timezone: UTC
<pre>
= TEXT( (Unixtime / 86400) + 25569, "YYYY-mm-dd hh:mm:ss")
</pre>

=== MySQL way: convert to date from unix timestamp ===
timezone: MySQL server timezone dependent {{exclaim}}<ref>[https://www.w3resource.com/mysql/date-and-time-functions/mysql-from_unixtime-function.php MySQL FROM_UNIXTIME() function]</ref>

<pre>
SELECT FROM_UNIXTIME(IF(`timestamp_column` = 0, NULL, `timestamp_column`, "%Y-%m-%d %H:%i:%S") 
</pre>

=== MySQL way: convert to unix timestamp from date time ===
Using [https://dev.mysql.com/doc/refman/8.0/en/date-and-time-functions.html#function_unix-timestamp UNIX_TIMESTAMP()] function

timezone: MySQL server timezone dependent {{exclaim}}

* {{kbd | key = SELECT UNIX_TIMESTAMP('2011-03-15 18:53:57');}} /* return timestamp: 1300186437 */
* {{kbd | key = SELECT UNIX_TIMESTAMP(STR_TO_DATE('2011-03-15 18:53:57', '%Y-%m-%d %H:%i:%S'));}} /* return timestamp: 1300186437 */

== References ==
<references />

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