User variables + SUM + GROUP BY = strange behavior

[Vadim P.]

Hello all,

 

Could anyone comment on User Variable behavior in the example below?

 

Thanks,

Vadim.

 

============================================================================
=

 

mysql> SELECT

    -> LEFT(CallTime,10) AS CallDate,

    -> @a := SUM(Charge),

    -> @b := SUM(Cost),

    -> @a - @b,

    -> @a,

    -> @b

    -> FROM Calls

    -> GROUP by CallDate

    -> ORDER BY CallDate DESC;

 

+------------+-------------------+-----------------+---------+--------+-----
-+

| CallDate   | @a := SUM(Charge) | @b := SUM(Cost) | @a - @b | @a     | @b
|

+------------+-------------------+-----------------+---------+--------+-----
-+

.

| 2004-03-01 |           621.059 |         249.310 |  30.882 | 39.512 | 8.63
|

| 2004-02-29 |            54.620 |          17.660 |  30.882 | 39.512 | 8.63
|

| 2004-02-28 |           205.581 |          17.460 |  30.882 | 39.512 | 8.63
|

| 2004-02-27 |           622.282 |         248.920 |  30.882 | 39.512 | 8.63
|

| 2004-02-26 |           607.274 |         277.100 |  30.882 | 39.512 | 8.63
|

| 2004-02-25 |           709.698 |         308.580 |  30.882 | 39.512 | 8.63
|

| 2004-02-24 |           783.210 |         298.560 |  30.882 | 39.512 | 8.63
|

| 2004-02-23 |           799.764 |         252.890 |  30.882 | 39.512 | 8.63
|

.