That's really not telling us anything about what you mean to do. If it's a standard custom field, then it already has a "connection" to the database, for it's configuration, data storage, and usage. So the word "connection" is too vague to form your question.
What are you actually trying to achieve? Why do you say "connect to database" or more importantly, why have you suggested that as an answer to what you're trying to do, without explaining the real goal?
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