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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'ac4ebebb4bf9fbb21f9c8c7cee62ff15e0b71d149987842392d687808af08b7c' 
  AND token = 'R6OkiVXw3XVCZipJ/tiYfj0cLEoE+SzITuTJiy1U0Pw=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00034

JSON explain

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