What is the difference between CHECKSUM_AGG() and CHECKSUM() ?
CHECKSUM calculates a hash for one or more values in a single row and returns an integer.
CHECKSUM_AGG is an aggregate function that takes a single integer value from multiple rows and calculates an aggregated checksum for each group.
They can be used together to checksum multiple columns in a group:
SELECT category, CHECKSUM_AGG(CHECKSUM(*)) AS checksum_for_category
FROM yourtable
GROUP BY category
CHECKSUM_AGG will perform a checksum across all the values that are being aggregated, coming up with a value.
It's typically used to see if a collection of values (in the group) has generally changed.
CHECKSUM is intended to build a hash index based on an expression or column list.
One example of using a CHECKSUM is to store the unique value for the entire row in a column for later comparison.
Related
I am trying to add a column to a collection by multiplying the 0.9 to existing database column recycling. but I get a run time error.
I tried to multiply 0.9 direction in the function but it is showing error, so I created the class and multiplied it there yet no use. what could be the problem?
Your error message is telling you what the problem is: your database query is using GROUP BY in an invalid way.
It doesn't make sense to group by one column and then select other columns (you've selected all columns in your case); what values would they contain, since you haven't grouped by them as well (and get one row returned per group)? You either have to group by all the columns you're selecting for, and/or use aggregates such as SUM for the non-grouped columns.
Perhaps you meant to ORDER BY that column (orderBy(dt.recycling.asc()) if ascending order in QueryDSL format), or to select all rows with a particular value of that column (where(dt.recycling.eq(55)) for example)?
I have a table which columns are location and credit, the location contains string rows which mainly is location_name and npl_of_location_name. the credit contains integer rows which mainly is credit_of_location_name and credit_npl_of_location_name. I need to make a column which calculates the ((odd rows of the credit - the even rows of the credit)*0.1). How do i do this?
When you specify "odd rows" and "even rows" are you referring to row numbers? Because, unless your query sorts the data, you have not control over row order; the database server returns rows however they are physically stored.
Once you are sure that your rows are properly sorted, then you can use a technique such as Mod(#INROWNUM,2) = 1 to determine "odd" and zero is even. This works best if the Transformer is executing in sequential mode; if it is executed in parallel mode then you need to use a partitioning algorithm that ensures that the odd and even rows for a particular location are in the same node.
I am new to tableau.
Just recently, I have encountered a problem regarding getting a string value from the previous row
I tried using Previous_Value function but it does not work. :<
Image of the error
Instead of previous value which could be tricky when dealing with partitions, you may use the LookUp function
Returns the value of the expression in a target row, specified as a relative offset from the current row. Use FIRST() +n and LAST() -n as part of your offset definition for a target relative to the first/last rows in the partition. If offset is omitted, the row to compare to can be set on the field menu. This function returns NULL if the target row cannot be determined.
You can create a calculated field Order ID Lookup - 1:
LOOKUP(max([Order ID]),-1)
Remember that Lookup requires an aggregate value as first argoment (in my example you can use either min, max, etc...) followed by the offset you need (in this example it's 1 for previous record).
Once you have your previous value, you can create another calculated field Check:
if max([Order ID]) = [Order ID Lookup - 1]
then '='
else '!='
end
Since Lookup needs an aggregate function, you should "wrap" your Order ID with an aggregation function as well in order to compare those 2 values.
Here's the final result:
This is the data that comes back from the database
Data Sample for one season (the report returns values for two):
What you can see is groupings, by Season, Theater then Performance number and lastly we have the revenue and ticket columns.
The SSRS Report Has three levels of groupings. Pkg (another ID that groups the below), venue -- the venue column and perf_desc -- the description column linked tot he perf_no.
Looks like this --
What I need to do is take the revenue column (a unique value) for each Performance and return it in a separate column -- so i use this formula.
sum(Max(Fields!perf_tix.Value, "perf_desc"))
This works great, gives me the total unique value for each performance -- and sums them up by the pkg level.
The catch is when i need to pull the data out by season.
I created a separate column looks like this
it's yellow because it's invisible and is referenced elsewhere. But the expression is if the Season value = to the Parameter (passed season value) -- then basically pull the sum of each of the tix values and sum them up. This also works great on the lower line - the line where the grouping exists for pkg -- light blue in my case.
=iif(Fields!season.Value = Parameters!season.Value, Sum(Max(Fields!perf_tix.Value, "perf_desc")), 0)
However, the line above -- the parent/header line its giving me the sum of the two seasons values. Basically adding it all up. This is not what I want and also why is it doing this. The season value is not equal to the passed parameter for the second season value so why is it adding it to the grouped value.
How do I fix this??
Since your aggregate function is inside your IIF function, only the first record in your dataset is being evaluated. If the first one matches the parameter, all records would be included.
This might work:
=IIF(Fields!season.Value = Parameters!season.Value, Sum(Max(Fields!perf_tix.Value, "perf_desc")), 0)
It might be better if your report was also grouping on the Venue, otherwise you count may include all values.
I'm trying to annualise my data in tableau, but get an error in the Calculated Field.
"Cannot mix aggregate and non-aggregate arguments to function"
my formula is
sum(profit)/month(selected date) *12
How do I get an integer for the current month? That seems to be the problem, it tries to aggregate the month as well.
Thanks.
Short answer: wrap the call to month in a call to min() -- which works well if you have MONTH([selected date]) on the visualization as a dimension.
There are three types of calculated fields in Tableau:
row level calculations which act on a single data row. They can read from values of other fields in the same row and return a single value per row.
aggregate calculations which act on a partition or block of data rows. They can reference the result of aggregating the values for a field across the entire partition, using a an aggregate function like SUM() or MIN().
table calculations which act on an entire table of aggregated results.
You can't mix and match. Everything in a calculated field must be all at one level or another -- either all referenced fields must use aggregation functions (for aggregate calculated fields) or no referenced fields must use aggregation functions (for data row level calculated fields).
Hence the error message you saw.
Sometimes you know that all values for a field will be the same in a partition based on your visualization, so the aggregation function seems unnecessary. But Tableau still requires you to be explicit about how to turn a block of values into a single value, because the calculation must be defined even when the visualization is partitioned differently. In these cases, you can use min(), max(), avg(), or perhaps attr() because they all return the same value for a list of identical values.
The first two types are typically executed on the server (i.e. they are implemented by Tableau emitting SQL to send to the database server). Table calculations are executed by Tableau on the client site to post-process the results from the database server.
Table calcs are the most complicated type, but can be very useful. Explaining them is a post for another day.