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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'c8894ea19196e80397504144da833551cd1b74e90a188715be3a5272c1c62497' 
  AND token = 'PKoLh5meBcjPq7hKZt6xDnQaMiMelFxo0kUgd5rKudM=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

JSON explain

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