permanently store balance result in a field of current table

[darendaren88]

I have created this table:

mysql> describe acount;
+----------+---------------+------+-----+---------+----------------+
| Field    | Type          | Null | Key | Default | Extra          |
+----------+---------------+------+-----+---------+----------------+
| uniqueID | bigint(20)    | NO   | PRI | NULL    | auto_increment |
| amount   | decimal(20,0) | NO   |     | NULL    |                |
| BALANCE  | decimal(20,2) | NO   |     | 0.00    |                |
+----------+---------------+------+-----+---------+----------------+
3 rows in set (0.04 sec)

and this are my current table:

mysql> select * from acount;
+----------+--------+---------+
| uniqueID | amount | BALANCE |
+----------+--------+---------+
|        8 |    200 |    0.00 |
|        9 |    100 |    0.00 |
|       10 |    200 |    0.00 |
|       11 |      5 |    0.00 |
|       12 |     13 |    0.00 |
|       13 |    145 |    0.00 |
|       14 |   -100 |    0.00 |
|       15 |    125 |    0.00 |
|       16 |     15 |    0.00 |
+----------+--------+---------+
9 rows in set (0.00 sec)

The problem is in the BALANCE field.It does no return any result.
When i enter this command:

mysql> SELECT uniqueID, amount, amount + coalesce( (
    ->
    -> SELECT sum( amount )
    -> FROM acount b
    -> WHERE b.uniqueID < a.uniqueID ) , 0
    -> ) AS BALANCE
    -> FROM acount a;
 

It will produce a table like this:

+----------+--------+---------+
| uniqueID | amount | BALANCE |
+----------+--------+---------+
|        8 |    200 |     200 |
|        9 |    100 |     300 |
|       10 |    200 |     500 |
|       11 |      5 |     505 |
|       12 |     13 |     518 |
|       13 |    145 |     663 |
|       14 |   -100 |     563 |
|       15 |    125 |     688 |
|       16 |     15 |     703 |
+----------+--------+---------+
9 rows in set (0.00 sec)

But I need the BALANCE table to permanently store the BALANCE result as table above.
when i check the balance field again, the result return to default value.

mysql> select balance from acount;
+---------+
| balance |
+---------+
|    0.00 |
|    0.00 |
|    0.00 |
|    0.00 |
|    0.00 |
|    0.00 |
|    0.00 |
|    0.00 |
|    0.00 |
+---------+
9 rows in set (0.00 sec

I need the balance to be update, automaticaly calculated and stored permanantly in the current table.
Just as table below:

+----------+--------+---------+
| uniqueID | amount | BALANCE |
+----------+--------+---------+
|        8 |    200 |     200 |
|        9 |    100 |     300 |
|       10 |    200 |     500 |
|       11 |      5 |     505 |
|       12 |     13 |     518 |
|       13 |    145 |     663 |
|       14 |   -100 |     563 |
|       15 |    125 |     688 |
|       16 |     15 |     703 |
+----------+--------+---------+

Can someone help me in this. Im totaly new in Mysql database.

[Atli]

Hey.

If you want to change the value of a field you need to use the UPDATE command.

The problem is that you can't run a sub-query from within an UPDATE command on the table being updated, which makes it very difficult to calculate the balance correctly using the UPDATE command alone.

Best I can come up with at the moment is creating a procedure that calculates this for you and use that to get the value for the balance field.

UPDATE myTable
    SET `balance` = GetBalance(`id`);

Where "GetBalance" is a function you create to calculate the balance.
(Check this out if you are new to procedures.)



You can avoid this problem altogether tho by adding this to the row when it is created.

The INSERT command can use the result set of a SELECT command as the values that are supposed to be inserted. You can use this to set the "balance" field of your new row as you INSERT it.
Like:

INSERT INTO `myTable`(`amount`, `balance`)
SELECT 10.00, IFNULL(SUM(`amount`) + 10.00, 10.00) FROM `myTable`;