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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b754d1b2aaa0a63699599249e36e3cd7461e91babe4bb17e64be942d321fd6b3' 
  AND token = 'PCSrigQ8L4uBBMKy8HOl7+MZ2DpMbJ/T8HU8ceWtd4U=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00054

JSON explain

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