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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '83421dad3d54afb2fee9a7b15e5b6a30457ee507b612c704a1c485bd0a06a958' 
  AND token = 'F9yiUwmJN9mJ5U5KpVSLKMYnf2dtrWv3eRl8x5WkW2I=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

JSON explain

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