How to do query and display the records until it reaches a certain number?
Suppose you want to select student until the total sum of the student's money reaches 1000?
Addition
Student ID Student Name Student Money
--------- ----------- --------------
1 John 190
2 Jenny 290
3 Ben 200
4 Andy 120
5 Lynna 300
If I wanna stop at 500, I would get record number 1 and 2 (190 + 290).
If I wanna stop at 1000, I would get record 1 until 4.
There is no "intrinsic" order to a SQL table, so you'll have to specify some ORDER BY clause to give that "until" phrase any meaning. Given that, the sum of the ``first'' N records can be obtained with a SELECT SUM(money) FROM student ORDER BY xxx LIMIT N. Using an auxiliary table INTS which has integers in natural order, you can find the maximum suitable N by something like:
SELECT MAX(N) FROM INTS
WHERE (SELECT SUM(money) FROM student ORDER BY xxx LIMIT N) < 1000
and finally insert this as another nested SELECT for the LIMIT clause in your overall SELECT. All of this smells like it would be rather inefficient, though! As often when nested SELECTs seem too many and too slow, an alternative is doing this in steps: first build a temporary table with the "progressive sums", then use that to help you find the limit you need.
Came across this question while searching for my own answer. I thought I'd leave my solution here since it's another way to accomplish the same task and may be more efficient. The trick is the self join using >=
SELECT s1.ID, s1.name, s1.money, sum(s2.money)
FROM student s1
INNER JOIN student s2 ON s1.id >= s2.id
GROUP BY s1.id HAVING SUM(s2.money) <= 500;
Oops ... MySQL ... this solution is for MS SQL ...
Here is a solution using the ROW_NUMBER() function.
SELECT Student.*, SUM(StudentBefore.Money) AS AccumulatedMoney
FROM (
SELECT *, ROW_NUMBER() OVER(ORDER BY Id) AS RowNumber
FROM Students
) AS Student
INNER JOIN
(
SELECT *, ROW_NUMBER() OVER(ORDER BY Id) AS RowNumber
FROM Students
) AS StudentBefore
ON StudentBefore.RowNumber <= Student.RowNumber
GROUP BY Student.RowNumber, Student.Id, Student.Name, Student.Money
HAVING SUM(StudentBefore.Money) < 1000
The execution plan indicates that sorting the table is the most expensive operation. If there is an index on the columns to sort by - you example indicates you want to sort by the primary key id - the index scan will become the most expensive operation.
