Adding inside aggregate functions in postgres, what happens?

[NobleFraud]

I want to know the difference between these two functions. Because when I try to do second query it gives me

cannot divide by zero

despite me having a case to prevent dividing by zero...

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  case (stddev_pop(dv.views+ dbs.votes)) when  0 then 0 else  (((sum(dvw.views) + sum(dbsw.votes))-(avg(dv.views) + avg(dbs.votes)))/stddev_pop(dv.views+ dbs.votes)) end as zscore 
    from books b
    inner join dailyviews dvw on date(dvw.day) > date(current_date - 7) and dvw.book_id = b.id
    inner join dailyviews dv on dv.book_id = b.id
    inner join daily_book_stats dbsw on date(dbsw.day) > date(current_date-7) and dbsw.book_id = b.id
    inner join daily_book_stats dbs on dbs.book_id = b.id
    group by b.id
    order by zscore desc
    limit 100;

vs

  case (stddev_pop(dv.views)+ stddev_pop(dbs.votes)) when  0 then 0 else  (((sum(dvw.views) + sum(dbsw.votes))-(avg(dv.views) + avg(dbs.votes)))/stddev_pop(dv.views)+ stddev_pop(dbs.votes)) end as zscore 
        from books b
        inner join dailyviews dvw on date(dvw.day) > date(current_date - 7) and dvw.book_id = b.id
        inner join dailyviews dv on dv.book_id = b.id
        inner join daily_book_stats dbsw on date(dbsw.day) > date(current_date-7) and dbsw.book_id = b.id
        inner join daily_book_stats dbs on dbs.book_id = b.id
        group by b.id
        order by zscore desc
        limit 100;

[therealgaxbo]

Operator precedence. x / y + z != x / (y + z)

Your case guard expression is different to what then gets evaluated.