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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'c8253b6e8a04861049916c5cdf70139c2fc17ee34a2909250ebc5da912589509' 
  AND token = 'bQ2rrTVHXzuBmebMwIxa4GDmnx3v09ocOMhF48asRQI=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00028

JSON explain

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