Hi, no, not directly. In BC online there's no access to the SQL database at all, Microsoft doesn't open it, not even read-only. So no SSMS, no connection string, nothing like that.
What you get instead are the APIs. The standard API v2.0 covers the common entities, and for anything else a developer makes a custom API page or API query in an extension, a small job usually. Power BI, Excel or any tool that speaks OData can read from those. For heavy reads there's the DataAccessIntent ReadOnly property on API pages and queries, then the request goes to the read replica and doesn't slow down the users.
If it's only for a quick look at the data, two tricks inside the client. Add ?table= with the table number to the URL to see the raw table, and analysis mode on list pages does a lot of what people want SQL for.
One caveat, APIs are not for pulling millions of rows every hour. For that volume you end in export to a lake anyway.
Glad to help - follow up if anything is unclear.
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Regards,
Grigorios Mavrogeorgis
Business Central Consultant & AL Developer
Work: Gmsoft Limited
Blog: insidebusinesscentral
LinkedIn: linkedin.com/in/gregorymavrogeorgis