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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '39d5dbbda759229618aed3f70535507e5a0341e1d86555a4fd7b8ef5083676e7' 
  AND token = '3JpuYkEfv26NtRUlLcW21N4ScSnZMifZhurc8KXfJA4=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

JSON explain

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