Current Day vs Previous Day in Table

Hello @iQuanti,

This can be accomplished through a SQL dataflow. 
You will have two transforms. 
Transform 1 will be to group your data down to a day view.

SELECT 

 `Date` 
,SUM(`Sales`) As 'Sales'  
,`Product`

FROM input_dataset

GROUP BY `Date`, `Product`

**Key notes

• We can add more columns into the Select statement. We need to ensure they are added in the GROUP BY as well as the JOIN of the next transform
• Your value column, (`sales` in this example) needs to have an aggregation. In this example I use SUM()
• If your Date column is a Date/Time we will need to remove the time value. This can be accomplished by wrapping your column in DATE(). -- DATE(`Date`) -- This will also need to be done in the group by. 
  
  

Transform 2 is were we join the data back onto itself. 

SELECT 

 a.`Date`
,a.`Sales` AS 'Current_Day'
,b.`Sales` As 'Previous_Day'
,a.`Product`

FROM transform_data_1 a

LEFT JOIN transform_data_1 b
ON a.`Date` = DATE_ADD(b.`Date`, INTERVAL 1 DAY)
AND a.`Product` = b.`Product`

Your output of your dataflow would simply be:

SELECT * FROM transform_data_2

This also works for other date comparisons. If you wanted to compare today vs same day last week, we would only change the time key word:

ON a.`Date` = DATE_ADD(b.`Date`, INTERVAL 1 DAY)

To:

ON a.`Date` = DATE_ADD(b.`Date`, INTERVAL 1 WEEK)

Doing a total for a week compared to total for last week would require a change in our Grouping as well as in the JOIN conditions.