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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51c6adfe8eabbfa4cb493f2c11a4f850b0eafb2dfda12d7b06b281fd9a26d995' 
  AND token = 'oZR8xdnKu4cFDp9QFvSeHdxixc2DMq9ii4Yn0wWkLpc=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00024

JSON explain

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