# Historian sql\_data\_ explain t\_stamp

**URL:** <https://forum.inductiveautomation.com/t/historian-sql-data--explain-t-stamp/5270>\
**Category:** Ignition\
**Created:** [October 12, 2012, 5:53pm UTC](https://forum.inductiveautomation.com/t/historian-sql-data--explain-t-stamp/5270 "2012-10-12T17:53:58Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![ecujak](https://avatars.discourse-cdn.com/v4/letter/e/839c29/32.png) [@ecujak](https://forum.inductiveautomation.com/u/ecujak)\
**Post date:** [October 12, 2012, 5:53pm UTC](https://forum.inductiveautomation.com/t/historian-sql-data--explain-t-stamp/5270/1 "2012-10-12T17:53:58Z")

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Historian sql\_data\_ explain t\_stamp

I am trying to query the history database and I need to know some things about this.

What does the bigint t\_stamp represent? How do I convert this into a date/time value?

Also, how often does this table update? Is this updated every change, every scan class interval, or ever scan class interval with a change from the previous value.

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<div class="post-metadata">

**Author:** ![Michael.Stofan](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/michael.stofan/32/3342_2.png) [@Michael.Stofan](https://forum.inductiveautomation.com/u/Michael.Stofan)\
**Post date:** [October 12, 2012, 6:13pm UTC](https://forum.inductiveautomation.com/t/historian-sql-data--explain-t-stamp/5270/2 "2012-10-12T18:13:59Z")

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The timestamp value in the SQLTags History tables are stored in Unix Time. It’s the number of milliseconds since January 1, 1970 00:00:00

To convert the timestamp, take a look at our knowledge base article here:  
[http://inductiveautomation.com/support/kb/142](http://inductiveautomation.com/support/kb/142)

As far as storing values, it depends on how you set everything up. The default is to store a value at every scanclass execution providing the value has changed since the last execution.

Hope this info was helpful.