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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '21e4d5a56f2d64855f42727e1555f9568dffd1fd5b15b8c95ad205b96295c6c3' 
  AND token = 'jrvOPLEdjLxY2dAKdPfYoB/MiceB1ls8MQj9DZ5Enzw=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00024

JSON explain

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