# "Document" Tag Logging on SQL Server ERROR

**URL:** <https://forum.inductiveautomation.com/t/document-tag-logging-on-sql-server-error/76050>\
**Category:** Ignition\
**Created:** [July 7, 2023, 10:15am UTC](https://forum.inductiveautomation.com/t/document-tag-logging-on-sql-server-error/76050 "2023-07-07T10:15:45Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![MarcoP](https://avatars.discourse-cdn.com/v4/letter/m/b9bd4f/32.png) [@MarcoP](https://forum.inductiveautomation.com/u/MarcoP)\
**Post date:** [July 7, 2023, 10:15am UTC](https://forum.inductiveautomation.com/t/document-tag-logging-on-sql-server-error/76050/1 "2023-07-07T10:15:45Z")

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Goodmorning,  
I have a complex object defined datatype to be logged on SQL Server through Ignition

![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/7/9/798df2d4c61622bf9ef3373f5228941ae11a2d2e.png)

![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/9/e/9eb7cbee2e89ccae280494ac304110efe6d092c5.png)

Document Tag (other typologies return error) correctly reads the value through OPC

![image](https://us1.discourse-cdn.com/inductiveautomation/original/3X/d/4/d462fcbbbbadb3c1e1c048563b3dbc2b092ecda8.png)

But it can't be logged on SQL Server and it's quarantined:  
ERROR: com.microsoft.sqlserver.jdbc.SQLServerException: Conversion from UNKNOWN to VARCHAR is not supported;

How can I fix?

Thank you and BR,  
Marco

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<div class="post-metadata">

**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\
**Post date:** [July 7, 2023, 10:57am UTC](https://forum.inductiveautomation.com/t/document-tag-logging-on-sql-server-error/76050/2 "2023-07-07T10:57:34Z")

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You cannot historize document or dataset tag types.

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<div class="post-metadata">

**Author:** ![MarcoP](https://avatars.discourse-cdn.com/v4/letter/m/b9bd4f/32.png) [@MarcoP](https://forum.inductiveautomation.com/u/MarcoP)\
**Post date:** [July 7, 2023, 11:26am UTC](https://forum.inductiveautomation.com/t/document-tag-logging-on-sql-server-error/76050/3 "2023-07-07T11:26:47Z")

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Thank you for response, neither by writing a custom script?

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<div class="post-metadata">

**Author:** ![pturmel](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/pturmel/32/3295_2.png) [@pturmel](https://forum.inductiveautomation.com/u/pturmel)\
**Post date:** [July 7, 2023, 11:48am UTC](https://forum.inductiveautomation.com/t/document-tag-logging-on-sql-server-error/76050/4 "2023-07-07T11:48:56Z")

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It isn't so much an Ignition problem as a limitation of generic JDBC. As in, not standardized. Many databases will accept document-style data as JSON, where you supply the string format to the DB. That can be scripted, but to your own DB tables, not to the historian.

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<div class="post-metadata">

**Author:** ![Kevin.Herron](https://sea1.discourse-cdn.com/inductiveautomation/user_avatar/forum.inductiveautomation.com/kevin.herron/32/7259_2.png) [@Kevin.Herron](https://forum.inductiveautomation.com/u/Kevin.Herron)\
**Post date:** [July 7, 2023, 2:04pm UTC](https://forum.inductiveautomation.com/t/document-tag-logging-on-sql-server-error/76050/5 "2023-07-07T14:04:40Z")

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Use expression or derived tags to pull the structure members into their own atomic tags, of a tag type that can be historized, and turn on history for those tags.