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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'cd4f2609b791e10697691554cf9940d15bff2459d52a208b39d6e3a4504ccc81' 
  AND token = 'Pcn7ny/AK7gTQ8NixEaBgDoOxY3/4F61OvlGCdnTFg8=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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