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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a39b1aef266f0cce6a0c2139a97538f3fc417417f0cab68e1eda85bf16551978' 
  AND token = '4JI0tXVeeRwwvM5DZYQG5fVwf3OOmuNMt1R4xGR6qU8=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

JSON explain

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