I am trying to fetch a SUM() for each user in a table, but MySQL is returning the wrong values.
This is how it should look (http://sqlfiddle.com/#!2/7b988/4/0)
user amount
110 20.898319244385
114 43.144836425781
115 20.487638473511
116 26.07483291626
117 93.054000854492
But this is how it does look (http://sqlfiddle.com/#!2/7b988/2/0)
user amount
110 167.186554
114 129.434509
115 143.413469
116 208.598663
117 744.432007
This is the query I am trying to run:
SELECT
blocks.user_id,
SUM(payout_history.amount) as amount
FROM blocks
LEFT JOIN payout_history
ON blocks.user_id = payout_history.user_id
WHERE confirms > 520
GROUP BY blocks.user_id
What am I doing wrong?
Try this query:
SELECT bl.user_id, SUM( ph.amount ) PAIDOUT
FROM (
SELECT distinct blocks.user_id
FROM blocks
WHERE confirms > 520
) bl
LEFT JOIN payout_history ph
ON bl.user_id = ph.user_id
GROUP BY ph.user_id
;
SQLFiddle --> http://sqlfiddle.com/#!2/7b988/48
--- EDIT --- an explanation how the query works (or rather why your query doesn't work) ----
Looking at expected results it seems that the query should calculate a sum of amount
column for each user_id
, but only for those user_id
, that are also in the blocks
table, and have a blocks.confirms
value grather than 520.
A simple join (also left outer join) cannot work in this case, because the blocks
table can contain many records for the same user_id
, for example a query that returns rows for only user_id=110
gives the following results:
SELECT *
FROM blocks
WHERE confirms > 520
AND user_id = 110;
+ ------- + ------------ + ----------- + ------------- +
| id | user_id | reward | confirms |
+ ------- + ------------ + ----------- + ------------- +
| 0 | 110 | 20.89832115 | 521 |
| 65174 | 110 | 3.80357075 | 698 |
| 65204 | 110 | 4.41933060 | 668 |
| 65218 | 110 | 4.69059801 | 654 |
| 65219 | 110 | 4.70222521 | 653 |
| 65230 | 110 | 4.82805490 | 642 |
| 65265 | 110 | 5.25058079 | 607 |
| 65316 | 110 | 6.17262650 | 556 |
+ ------- + ------------ + ----------- + ------------- +
The straigh join (and LEFT/RIGHT outer join) works in this way, that takes each record from the first joinded table, and pair this record (combine it) with all rows from the other joinded table thet meet the join condition.
In our case the left join produces a below resultset:
SELECT *
FROM blocks
LEFT JOIN payout_history
ON blocks.user_id = payout_history.user_id
WHERE confirms > 520
AND blocks.user_id = 110;
+ ------- + ------- + ----------- + -------- + --- + ------- + ----------- +
| id | user_id | reward | confirms | id | user_id | amount |
+ ------- + ------- + ----------- + -------- + --- + ------- + ----------- +
| 0 | 110 | 20.89832115 | 521 | 1 | 110 | 20.898319 |
| 65174 | 110 | 3.80357075 | 698 | 1 | 110 | 20.898319 |
| 65204 | 110 | 4.41933060 | 668 | 1 | 110 | 20.898319 |
| 65218 | 110 | 4.69059801 | 654 | 1 | 110 | 20.898319 |
| 65219 | 110 | 4.70222521 | 653 | 1 | 110 | 20.898319 |
| 65230 | 110 | 4.82805490 | 642 | 1 | 110 | 20.898319 |
| 65265 | 110 | 5.25058079 | 607 | 1 | 110 | 20.898319 |
| 65316 | 110 | 6.17262650 | 556 | 1 | 110 | 20.898319 |
+ ------- + ------- + ----------- + -------- + --- + ------- + ----------- +
and now if we add SUM( amount ) .... GROUP BY user_id
, MySql will calucate a sum of all amount
values from the above resultset ( 8 rows * 20.898 = ~ 167.184 )
SELECT blocks.user_id, sum( amount)
FROM blocks
LEFT JOIN payout_history
ON blocks.user_id = payout_history.user_id
WHERE confirms > 520
AND blocks.user_id = 110
GROUP BY blocks.user_id;
+ ------------ + ----------------- +
| user_id | sum( amount) |
+ ------------ + ----------------- +
| 110 | 167.186554 |
+ ------------ + ----------------- +
As you see in this case the join doesn't give us desired results - we need something named a semi join
- below are different variants of semi joins, give them a try:
SELECT bl.user_id, SUM( ph.amount ) PAIDOUT
FROM (
SELECT distinct blocks.user_id
FROM blocks
WHERE confirms > 520
) bl
LEFT JOIN payout_history ph
ON bl.user_id = ph.user_id
GROUP BY ph.user_id
;
SELECT ph.user_id, SUM( ph.amount ) PAIDOUT
FROM payout_history ph
WHERE ph.user_id IN (
SELECT user_id FROM blocks
WHERE confirms > 520
)
GROUP BY ph.user_id
;
SELECT ph.user_id, SUM( ph.amount ) PAIDOUT
FROM payout_history ph
WHERE EXISTS (
SELECT 1 FROM blocks bl
WHERE bl.user_id = ph.user_id
AND bl.confirms > 520
)
GROUP BY ph.user_id
;
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With