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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51ad6a7fcfc8d7f7aa3ffe30dadf4d0f03b01793bd7d5eebf04c52af22b58beb' 
  AND token = 'OD8ZS4QaVfkb+TupQ3tGyXkvrCf7DYyIHX8i1YOij98=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00035

JSON explain

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