How to create a partial balance row by row in SQL - mysql

Question

I ‘m trying to do a query with a partial balance, where the last column is a sum row by row:
Here a set of data A, the date is DD-MM-YYYY
Amount | Date
20 | 16-01-2013
-1 | 22-01-2013
-2 | 22-01-2013
-3 | 23-01-2013
-9 | 24-01-2013
Here a set of data B
Amount | Date
-5 | 23-01-2013
-4 | 23-01-2013
9 | 23-01-2013
3 | 24-01-2013
-3 | 24-01-2013
I’d like to have a result like this, let's say for the set of data A:
Amount | Date | Balance
-9 | 24-01-2013 | 14
-3 | 23-01-2013 | 17
-2 | 22-01-2013 | 19
-1 | 22-01-2013 | 20
20 | 16-01-2013 | 0
I'm using this query for both data set:
SELECT
PreAgg.tData,
PreAgg.amount,
#PrevBal := #PrevBal - PreAgg.amount AS Total
FROM
(
SELECT
pr.tData,
pr.amount
FROM
tableTest pr
ORDER BY
pr.tData desc
) AS PreAgg,
(SELECT #PrevBal := 0.00) AS SqlVars
Well for the data set B it works perfect for the data set A it doesn't, and I cannot understand why!
thank a lot
SOLUTION
Hi at the end I managed to do it.
I use a fake counter here the query:
SELECT
reference,amount,balance
FROM
(
SELECT
#id := #id + 1 AS id,t.date as reference,t.amount,
#balance := (#balance + t.amount) AS balance
FROM
tmpTable t, (SELECT #id:=0, #balance:=0, #grouping:=0) AS vars
ORDER BY
t.tData
) AS x
ORDER BY
x.id DESC

Answer 1

Your result only makes sense if I interpret the dates as DD-MM-YYYY. Otherwise, the dates are garbled.
Assuming the dates are stored as dates (and not strings), you want "asc" instead of "desc":
SELECT (#rownumIn :=amount+#rownumIn) AS Balance, date, amount
FROM table_data cross join
(SELECT #rownumIn := 0
) AS counter
WHERE some constraits
ORDER BY date asc;
I suspect you have committed the sin of storing dates as strings, though. If this is the case, it is easily fixed using str_to_date():
SELECT (#rownumIn :=amount+#rownumIn) AS Balance, date, amount
FROM table_data cross join
(SELECT #rownumIn := 0
) AS counter
WHERE some constraits
ORDER BY str_to_date(date, '%d-%m-%Y') asc;