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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b8421b1e85e1543f9f6befc3af4cc684d7463aef5f185cf654798bb1b4ba5587' 
  AND token = '8eErGg1dejNgqMjaatHwxs45uqjYi7ZAOy+TLI8+g5w=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00033

JSON explain

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