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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b21d767e257e9835ac488bddca9f9c3cea14f996337e4a6d81beacbb79474c92' 
  AND token = 'UJkZWVlwmEsinc6AV5ghzRd8mX40AlrIg2IA7rDN8YM=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00029

JSON explain

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