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Sum Expression

Sum(expression) is a common usage in SQL and is often needed by various data analysis scenarios.

In the previous versions, table index or computed column is required for sum(expression) to work. Since v5, Kylin can answer some kind of sum(expression) using model.

How to Use​

This feature is off by default. To enable it, please set the configuration in $KYLIN_HOME/conf/kylin.properties.

kylin.query.convert-sum-expression-enabled=true

Currently, four kinds of sum (expression) usages are supported, namely

  • sum(case when)
  • sum(column*constant)
  • sum(constant)
  • sum(cast(case when))

We will use the sample dataset to introduce the usage. Read more about the Sample Dataset.

sum(case when) function

For example:

select
  sum(case when LO_ORDERPRIOTITY='1-URGENT' then LO_ORDTOTALPRICE else null end)
from SSB.LO_LINEORDER

In order to run this SQL, set your model as below in addition to enable sum(expression):

  • Define all columns in the when clause as dimensions, like the LO_ORDERPRIOTITY in this example.
  • Define all columns in the then clause as Sum measure, like the sum(LO_ORDTOTALPRICE) in this example.

Then, the model will be able to run the above SQL.

sum(column*constant) function

For example:

select sum(LO_ORDTOTALPRICE * 3) from SSB.LO_LINEORDER

In order to run this SQL, set your model as below in addition to enable sum(expression):

  • Define the column in the sum function as Sum measure, like the sum(LO_ORDTOTALPRICE) in this example.

Then, the model will be able to run the above SQL.

sum(constant) function

For example:

select sum(3) from P_LINEORDER

In order to run this SQL, just enable the sum(expression) feature. No other setting on model is needed.

sum(cast(case when)) function

For example:

select sum(cast((case when LO_ORDERPRIOTITY='1-URGENT' then LO_ORDTOTALPRICE else null end) as bigint)) from SSB.P_LINEORDER

In order to run this SQL, set your model as below in addition to enable sum(expression):

  • Define all columns in the when clause as dimensions, like the ORDERPRIOTITY in this example.
  • Define all columns in the then clause as Sum measure, like the sum(ORDTOTALPRICE) in this example.

Then, the model will be able to run the above SQL.

Known Limitation​

  1. Due to the complexity of null value, sum(column+column) and sum(column+constant) are not supported yet. If you need use the above syntax, please use computed column or table index.
  2. In the current version, topN is not supported to use together with sum(case when). count(distinct), collect_set, percentile can be used with sum(case when)，but they can not be answered by single index.