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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '21db0a0270f80ebe3dd1e3971c7d3d6832cf8b6bcfe66af8bf8e84fd8047c160' 
  AND token = 'xDQMFxJ+Eo8zjwd3uYauWJvV8NDsl+1SqDyp6uuCB2c=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00041

JSON explain

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