Temporal Tables and History Retention

I’m a huge fan of Temporal Tables in SQL Server 2016. I first wrote about them, in a four-part series in November 2015, before SQL Server was even released. I don’t always get this excited about new features.

However, it has some limitations. As part of this week’s T-SQL Tuesday, hosted by the attractive and humble Brent Ozar, I have discovered a Microsoft Connect item I feel very strongly about.

Adam Machanic, the creator of an indispensable tool, sp_WhoIsActive, has created a Connect item entitled Temporal Tables: Improve History Retention of Dropped Columns.

As my readers know, temporal tables have to have the same schema as their base tables (the number and order of columns, and their respective data types, have to match).

Where this breaks down is when a table structure has changed on the base table. The history table also needs to take those changes into account, which could potentially result in data loss or redundant columns in the base table.

Adam suggests allowing columns which no longer appear in the base table to be retained in the history table and marked as nullable (or hidden), and should only appear when performing a point-in-time query by referring to the column(s) explicitly.

I have voted for this suggestion, and at the time of writing, it has 16 upvotes. I encourage you to add your voice to this suggestion.

If you have any other suggestions, or wish to discuss temporal tables, please contact me on Twitter at @bornsql .

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