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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b2f893d00eaf76882e76451eb30974694608d6b3fb59bd7edb5a629088319a34' 
  AND token = '5/BEblqhpSUiwDcDETUEbUNkGwvFy9RcGkjaDPm2k0Q=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00024

JSON explain

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