Question

This is a follow up from my question: “MySQL: Querying a table and possibly replacing some fields with values from another table”

I have two tables. Table1 is our main table of data and Table2 has a subset of the Table1 columns and a subset of the records contained in Table1. You can see Table2 as a table holding corrected values for some of Table1’s records.

Here are my tables with sample data:

Table1

| page_id | field_id | date       | value | bla   |
--------------------------------------------------|
|     1   |      1   | 2012-01-01 |   3   |   1   |
|     2   |      1   | 2012-01-01 |   10  |   2   |
|     3   |      1   | 2012-01-01 |   25  |   2   |
|     1   |      2   | 2012-01-01 |   11  |   3   |
|     2   |      2   | 2012-01-01 |   22  |   1   |
|     3   |      2   | 2012-01-01 |   33  |   2   |

Table2

| page_id | field_id | date       | value | 
-------------------------------------------
|     1   |      1   | 2012-01-01 |   1   |
|     2   |      1   | 2012-01-01 |   2   |
|     3   |      1   | 2012-01-01 |   3   |
|     4   |      1   | 2012-01-01 |   4   |

I want to calculate the sum of values for one or more field_ids, following these rules:

(1) If records for one of the specified field_id exists only in Table1, I want to sum both value and bla for all records where field_id match the specified field_id

(2) If the field_id exists in both Table1 and Table2, then we would get the sum of value from Table2 and the sum of bla from Table1.

Here is the query I am using:

SELECT t1.field_id,
SUM(IFNULL(t2.value, IFNULL(t1.value,0))) as 'Value Sum',
SUM(IFNULL(t1.bla,0)) as 'Bla Sum'
FROM test.Table1 t1
LEFT JOIN test.Table2 t2 ON t1.field_id = t2.field_id
WHERE (t1.field_id IN (1,2))
GROUP BY t1.field_id, t1.date;

But I am not getting the correct sums for field_1:

|field_id | Value Sum  | Bla Sum| 
---------------------------------
|      1  |      30    |   20   | <-- was expecting 10 and 5, respectively 
|      2  |      66    |    6   |

Would you have any idea what I could be doing wrong?

Thanks in advance!

Answer 1

You need to add also the page_id to the JOIN otherwise the 3 row from table1 and 4 of table2 for field_id1 result in 12 columns

SELECT t1.field_id,
SUM(IFNULL(t2.value, IFNULL(t1.value,0))) as 'Value Sum',
SUM(IFNULL(t1.bla,0)) as 'Bla Sum'
FROM test.Table1 t1
LEFT JOIN test.Table2 t2 ON t1.field_id = t2.field_id AND t1.page_id =t2.page_id
WHERE t1.field_id IN (1,2)
GROUP BY t1.field_id;

also removed the group by t1.date