What can be done to force the following query to return a single row of data?

```
> SELECT integral(P49), mean(P49), count(P49), min(P49), max(P49) FROM L2 WHERE time >= NOW() - 604800s AND time<NOW()
name: L2
time integral mean count min max
---- -------- ---- ----- --- ---
0 878064.1014254978
1536760367611843633 1.4520673051503423 3359 0.280718 7.91543
```

As seen, if integral is performed separately, it returns a single row.

```
> SELECT mean(P49), count(P49), min(P49), max(P49) FROM L2 WHERE time >= NOW() - 604800s AND time<NOW()
name: L2
time mean count min max
---- ---- ----- --- ---
1536760369666651138 1.4520673051503423 3359 0.280718 7.91543
> SELECT integral(P49) FROM L2 WHERE time >= NOW() - 604800s AND time<NOW()
name: L2
time integral
---- --------
0 878064.1014254978
>
```