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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '39461d241a91ca030efb2e97d9021c556f13743a684bc5c903796131e9bca894' 
  AND token = 'fCSHOeSuW1I4tvGtztpecLaknpymExCm8CmWhlbgdZA=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00024

JSON explain

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