Hi, Imogen

Thanks for reaching out to us

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The most important detail i have to point out is,  when you say that you maintain a Spreadsheet,

if this Spreadsheet is connected/linked with a table in our plugin, in this case it will not make a new table in your MySQL database, so a separate Database connection will not be useful in that regard.

The separate DB connections are used when you make SQL Tables.

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For linking tables with a Google Spreadsheet - you will be able to link the same Spreadsheet on multiple sites,

if you share the access to the Spreadsheet with another company, they should have no issue of making a table from it on their site,

and the data is going to sync in the same way for a table on your site and for a table on another site.

Important to note, about the "update interval",

when you modify or add new rows on the source Google sheet,

 the plugin will show those changes within 15 minutes (since there's cache on Google's side). More details here. 

If you don't want to face any issues with cache, you can use the Google Sheets API method. ( more details here-)

We also have our own caching and auto-update cache feature, that you can use to make a custom update time interval with Cron jobs.

2.  But, if you wish to import this Google Spreadsheet to make a new Manual Table, then a new table gets created in your database,  and it loses the connection to the source Google Spreadsheet.

If you wish to update an existing Manual table from the Spreadsheet > Then you have to upload the data into the table from our plugin. More details on updating Manual tables from source data here.

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Let me know if this information helps, and if i perhaps misunderstood your use-case. Thank you