SUM Function

SUM([DISTINCT | ALL] expression) [OVER (analytic_clause)]

-- Total all the values for this column in the table.
select sum(c1) from t1;
-- Find the total for this column from a subset of the table.
select sum(c1) from t1 where month = 'January' and year = '2013';
-- Find the total from a set of numeric function results.
select sum(length(s)) from t1;
-- Often used with functions that return predefined values to compute a score.
select sum(case when grade = 'A' then 1.0 when grade = 'B' then 0.75 else 0) as class_honors from test_scores;
-- Can also be used in combination with DISTINCT and/or GROUP BY.
-- Return more than one result.
select month, year, sum(purchase_price) from store_stats group by month, year;
-- Filter the input to eliminate duplicates before performing the calculation.
select sum(distinct x) from t1;

The following examples show how to use SUM() in an analytic context. They use a table containing integers from 1 to 10. Notice how the SUM() is reported for each input value, as opposed to the GROUP BY clause which condenses the result set.

select x, property, sum(x) over (partition by property) as sum from int_t where property in ('odd','even');
+----+----------+-----+
| x  | property | sum |
+----+----------+-----+
| 2  | even     | 30  |
| 4  | even     | 30  |
| 6  | even     | 30  |
| 8  | even     | 30  |
| 10 | even     | 30  |
| 1  | odd      | 25  |
| 3  | odd      | 25  |
| 5  | odd      | 25  |
| 7  | odd      | 25  |
| 9  | odd      | 25  |
+----+----------+-----+

Adding an ORDER BY clause lets you experiment with results that are cumulative or apply to a moving set of rows (the "window"). The following examples use SUM() in an analytic context (that is, with an OVER() clause) to produce a running total of all the even values, then a running total of all the odd values. The basic ORDER BY x clause implicitly activates a window clause of RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW, which is effectively the same as ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW, therefore all of these examples produce the same results:

select x, property,
  sum(x) over (partition by property order by x) as 'cumulative total'
  from int_t where property in ('odd','even');
+----+----------+------------------+
| x  | property | cumulative total |
+----+----------+------------------+
| 2  | even     | 2                |
| 4  | even     | 6                |
| 6  | even     | 12               |
| 8  | even     | 20               |
| 10 | even     | 30               |
| 1  | odd      | 1                |
| 3  | odd      | 4                |
| 5  | odd      | 9                |
| 7  | odd      | 16               |
| 9  | odd      | 25               |
+----+----------+------------------+

select x, property,
  sum(x) over
  (
    partition by property
    order by x
    range between unbounded preceding and current row
  ) as 'cumulative total'
from int_t where property in ('odd','even');
+----+----------+------------------+
| x  | property | cumulative total |
+----+----------+------------------+
| 2  | even     | 2                |
| 4  | even     | 6                |
| 6  | even     | 12               |
| 8  | even     | 20               |
| 10 | even     | 30               |
| 1  | odd      | 1                |
| 3  | odd      | 4                |
| 5  | odd      | 9                |
| 7  | odd      | 16               |
| 9  | odd      | 25               |
+----+----------+------------------+

select x, property,
  sum(x) over
  (
    partition by property
    order by x
    rows between unbounded preceding and current row
  ) as 'cumulative total'
  from int_t where property in ('odd','even');
+----+----------+------------------+
| x  | property | cumulative total |
+----+----------+------------------+
| 2  | even     | 2                |
| 4  | even     | 6                |
| 6  | even     | 12               |
| 8  | even     | 20               |
| 10 | even     | 30               |
| 1  | odd      | 1                |
| 3  | odd      | 4                |
| 5  | odd      | 9                |
| 7  | odd      | 16               |
| 9  | odd      | 25               |
+----+----------+------------------+

Changing the direction of the ORDER BY clause causes the intermediate results of the cumulative total to be calculated in a different order:

select sum(x) over (partition by property order by x desc) as 'cumulative total'
  from int_t where property in ('odd','even');
+----+----------+------------------+
| x  | property | cumulative total |
+----+----------+------------------+
| 10 | even     | 10               |
| 8  | even     | 18               |
| 6  | even     | 24               |
| 4  | even     | 28               |
| 2  | even     | 30               |
| 9  | odd      | 9                |
| 7  | odd      | 16               |
| 5  | odd      | 21               |
| 3  | odd      | 24               |
| 1  | odd      | 25               |
+----+----------+------------------+

The following examples show how to construct a moving window, with a running total taking into account 1 row before and 1 row after the current row, within the same partition (all the even values or all the odd values). Because of a restriction in the Impala RANGE syntax, this type of moving window is possible with the ROWS BETWEEN clause but not the RANGE BETWEEN clause:

select x, property,
  sum(x) over
  (
    partition by property
    order by x
    rows between 1 preceding and 1 following
  ) as 'moving total'
  from int_t where property in ('odd','even');
+----+----------+--------------+
| x  | property | moving total |
+----+----------+--------------+
| 2  | even     | 6            |
| 4  | even     | 12           |
| 6  | even     | 18           |
| 8  | even     | 24           |
| 10 | even     | 18           |
| 1  | odd      | 4            |
| 3  | odd      | 9            |
| 5  | odd      | 15           |
| 7  | odd      | 21           |
| 9  | odd      | 16           |
+----+----------+--------------+

-- Doesn't work because of syntax restriction on RANGE clause.
select x, property,
  sum(x) over
  (
    partition by property
    order by x
    range between 1 preceding and 1 following
  ) as 'moving total'
from int_t where property in ('odd','even');
ERROR: AnalysisException: RANGE is only supported with both the lower and upper bounds UNBOUNDED or one UNBOUNDED and the other CURRENT ROW.