# Date arithmetics

Group by day of the week (using arithmetic).

schema:gisq

We can use modular arithmetic to calculate the day of the week.

We happen to know that 20 May 1962 was a Sunday. We calculate the number of days from that day and take mod 7 value. This tells us the day of the week: 0 is Sunday, 1 is Monday...

```
SELECT MOD(wk - TO_DATE('1962-05-20','YYYY-MM-DD'),7),
COUNT(song)
FROM gisq.totp
GROUP BY MOD(wk - TO_DATE('1962-05-20','YYYY-MM-DD'),7)
```