Insert SQL on based on field from ALL records

I have seen this done when moving a table, but it uses the entire select subquery as the values input. I need to do something similar to this:

INSERT INTO customer_alerts
  (message, customer_id) 
VALUES 
  ("Message HERE", (SELECT Customer.id from Custom开发者_如何学Goers as Customer))

Any ideas on how to achieve this?

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Use:

INSERT INTO customer_alerts
  (message, customer_id) 
SELECT 'Message HERE', c.id 
  FROM CUSTOMERS c

You can statically define values in the SELECT clause.