How do I calculate a running SUM on a SQLite query?

问题

How do I get a column that is the sum of all the values before of another column?

回答1:

You can do it by joining the table with itself (performing a so-called Cartesian or cross join). See the following example.

SELECT a.name, a.gdppc, SUM(b.gdppc)
FROM gdppc AS a, gdppc AS b WHERE b.gdppc <= a.gdppc 
GROUP BY b.id ORDER BY a.gdppc;

Given a table containing countries and their per capita GDP it will give you a running total of the GDP figure.

Democratic Republic of Congo|329.645|329.645
Zimbabwe|370.465|700.11
Liberia|385.417|1085.527
Burundi|399.657|1485.184
Eritrea|678.954|2164.138
Niger|711.877|2876.015
Central African Republic|743.945|3619.96
Sierra Leone|781.594|4401.554
Togo|833.803|5235.357
Malawi|867.063|6102.42
Mozambique|932.511|7034.931
...

Note that this can be a very resource-intensive operation, because if a table has N elements it will create a temporary table with N*N elements. I would not perform it on a large table.

回答2:

Cross join solutions like Diomidis Spinellis suggested take O(N^2) time. A recursive CTE can work faster, if you can stomach the convoluted code.

This produces the same output as his.

WITH RECURSIVE running(id, name, gdppc, rt) AS (
    SELECT row1._rowid_, row1.name, row1.gdppc, COALESCE(row1.gdppc,0)
    FROM gdppc AS row1
    WHERE row1._rowid_ = (
        SELECT a._rowid_
        FROM gdppc AS a
        ORDER BY a.gdppc, a.name, a._rowid_
        LIMIT 1)
    UNION ALL
    SELECT row_n._rowid_, row_n.name, row_n.gdppc, COALESCE(row_n.gdppc,0)+running.rt
    FROM gdppc AS row_n INNER JOIN running
    ON row_n._rowid_ = (
        SELECT a._rowid_
        FROM gdppc AS a
        WHERE (a.gdppc, a.name, a._rowid_) > (running.gdppc, running.name, running.id)
        ORDER BY a.gdppc, a.name, a._rowid_
        LIMIT 1))
SELECT running.name, running.gdppc, running.rt
FROM running;

Ordering and comparisons take care of duplicates, COALESCE is there to ignore NULLs.

If you have a good index, this should be O(N log N). Since SQLite doesn't support cursors, an O(N) solution probably doesn't exist without relying on an external application.

回答3:

As of SQLite 3.25.0, since 2018-09-15, window functions and their keyword OVER are supported. The answer to your question is now easy:

SELECT Country, Gdp, SUM(Gdp) OVER (ROWS UNBOUNDED PRECEDING)
FROM CountryGdp;

This is the minimal query that does what you request, but it doesn't define any ordering so here is a more proper way of doing it.

SELECT
    Country,
    Gdp,
    SUM(Gdp) OVER (
        ORDER BY Country -- Window ordering (not necessarily the same as result ordering!)
        ROWS BETWEEN -- Window for the SUM includes these rows:
            UNBOUNDED PRECEDING -- all rows before current one in window ordering
            AND CURRENT ROW -- up to and including current row.
        ) AS RunningTotal
FROM CountryGdp
ORDER BY Country;

In any way, the query should run in O(N) time.

回答4:

You have to do a sum in the field you want.... The query depends on the database you're using, Oracle allows you to do this:

select id, value, sum(value) as partial_sum over (order by id) from table

来源：https://stackoverflow.com/questions/5606560/how-do-i-calculate-a-running-sum-on-a-sqlite-query

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