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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '21c6671294517f16f8dffc736e6f3265eb85b4cbf185b92968695f78ba624c15' 
  AND token = '6bjpffXjDJX0x7/vEgCPdXokyWtynJBBf3JXUInqhsA=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

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