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I have a table like : trans is the name of the table for example
Id | Trans_Date | Account_Id | Amount | Delta
------------------------------------------------------
1 | 2011-02-20 00:00:00 | 2 | 1200 | NULL
------------------------------------------------------
2 | 2011-03-21 00:00:00 | 2 | 2000 | NULL
------------------------------------------------------
3 | 2011-04-22 00:00:00 | 2 | 4500 | NULL
------------------------------------------------------
4 | 2011-02-20 00:00:00 | 4 | 1000 | NULL
------------------------------------------------------
5 | 2011-03-21 00:00:00 | 4 | 2400 | NULL
------------------------------------------------------
6 | 2011-04-22 00:00:00 | 4 | 3000 | NULL
------------------------------------------------------
And I have to update Delta column. which value is the difference of current row of the same account and preceeding row of the same account assuming there is one transaction per month. Here is a dummy sql which can generate the delta value
select tt1.id, tt1.amount , tt1.AccountId,(tt1.amount-tt2.amount) as delta
from trans tt1 left outer JOIN trans tt2
on tt1.accountid = tt2.accountid
where month(tt1.date1)-month(tt2.date1)=1 ;
The result of this query is
id | amount | AccountId | delta |
-------------------------------------
2 | 2000 | 2 | 800 |
-------------------------------------
3 | 4500 | 2 | 2500 |
-------------------------------------
5 | 2400 | 4 | 1400 |
-------------------------------------
6 | 3000 | 4 | 600 |
-------------------------------------
But the delta of the row which has not any preceeding row should be its amount such as
1 | 1200 | 2 | 1200 |
-----------------------------------------
4 | 1000 | 4 | 1000 |
-----------------------------------------
these are missing by the way.
Please help me in resolving this query.
632
To calculate a difference, you need a pair of records; those two records are “the current record” and “the previous year's record”. You obtain this record using the LAG() window function. This function allows you to obtain data from the previous record (based on an order criterion, which here is “ ORDER BY year ”).
SQL Server DIFFERENCE() Function The DIFFERENCE() function compares two SOUNDEX values, and returns an integer. The integer value indicates the match for the two SOUNDEX values, from 0 to 4. 0 indicates weak or no similarity between the SOUNDEX values.
Here's the SQL query to compare each row with previous row. In the above query, we join sales table with itself using an INNER JOIN condition g2.id=g1.id + 1 that allows you to compare each row with its previous row. Please note, this condition depends on the fact that our id column has consecutive numbers.
1) You can use MAX or MIN along with OVER clause and add extra condition to it. The extra condition is "ROWS BETWEEN 1 PRECEDING AND 1 PRECEDING" which will fetch previous row value. Check this: SELECT *,MIN(JoiningDate) OVER (ORDER BY JoiningDate ROWS BETWEEN 1 PRECEDING AND 1 PRECEDING) AS EndDate.
Here's your original query modified accordingly:
select
tt1.id,
tt1.amount,
tt1.AccountId,
(tt1.amount-ifnull(tt2.amount, 0)) as delta
from trans tt1
left outer JOIN trans tt2 on tt1.accountid = tt2.accountid
and month(tt1.date1)-month(tt2.date1)=1;
The month comparison is moved from where to on, which makes a difference for left join, and tt2.amount is replaced with ifnull(tt2.amount, 0).
The UPDATE version of the script:
update tt1
set delta = (tt1.amount-ifnull(tt2.amount, 0))
from trans tt1
left outer JOIN trans tt2 on tt1.accountid = tt2.accountid
and month(tt1.date1)-month(tt2.date1)=1;
The correct MySQL syntax for the above update should actually be:
update trans tt1
left outer JOIN trans tt2
on tt1.accountid = tt2.accountid
and month(tt1.date1)-month(tt2.date1)=1
set tt1.delta = (tt1.amount-ifnull(tt2.amount, 0));
(Thanks @pinkb.)
105
You can use an inner query, but it's not necessarily the most efficient query.
UPDATE trans
SET Delta = Amount -
(SELECT Amount FROM trans t1
WHERE t1.Trans_Date < trans.Trans_Date
ORDER BY t1.Trans_Date DESC LIMIT 1)
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