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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'af51f251ece64514652e814c6d3ff3256d2a8e7762184049b2539ce537520e32' 
  AND token = 'MyLWEbKd29gjgOtXIT4N7T8z9lfLHRvA6d/f9BZNwRo=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}