Update your _config.yml to define your data sources with your SQLite database.

...
sqlite:
  - data: customers
    file: *db
    query: SELECT * from Customers

Then, you can use the site.data attributes accordingly:

{{ site.data.customers | jsonify }}

Output targets

A query can write to one of two targets:

• data: — attaches results to site.data (or page.data for per-page queries). Use this when the data is consumed by your own templates.
• collection: — appends results as documents to a Jekyll collection, including the special built-in posts collection. Use this when you want each row to become a page, or when you want existing Jekyll plugins (pagination, feed, sitemap, categories) to pick up the data automatically.

See Writing to Collections for the collection form.