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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a8840451edbaa2cbc7fcfa9a003988e59a6fad8fcdf825c2d04db764c25af37c' 
  AND token = '52j5nbKxQLNScNr/C48kCRhDfyeS6uMQat/UtpjD/N8=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

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