can't store the login &logout correctly

so here is what i've got so far

mysqli_query($coection, "INSERT INTO user_stat(useame, logout) VALUES ('$_SESSION[useame]', NOW())"); //  the query for storing the logout at logout.php 

and

mysqli_query($coection, "INSERT INTO user_stat(useame, logintime) VALUES ('$_SESSION[useame]', NOW())"); //  the query for storing the login time at login.php

I've managed to store the values in the database but not in the same row. Here is what they look like in the table user_stat table in db

Is there anyone who could help a little with this struggle

Thanks in advance :)