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Cardinality

Definition​

The cardinality method allows you to add the CARDINALITY function to the query. The CARDINALITY function is used to returns the total number of elements in the array, or 0 if the array is empty.

There are 2 ways to call this method:

1. Calling from a KColumn or a KTableColumn​

The only one method available to use this functionality calling from a KColumn or a KTableColumn is:

  • cardinality(): It does not receive any parameters. The KColumn or KTableColumn that invokes the method will be the one supplied to the CARDINALITY function.

Example​

Java code:

k
.select(
    APP_USER.EMAIL.arrayAgg().cardinality(),
    APP_USER.CREATED_AT.cast(date())
)
.from(APP_USER)
.groupBy(APP_USER.CREATED_AT.cast(date()))
.multiple();

SQL generated:

SELECT
    CARDINALITY(ARRAY_AGG(au.email)),
    CAST(au.created_at AS DATE)
FROM app_user au
GROUP BY CAST(au.created_at AS DATE)

Parameters:

  • None

2. Calling from the KFunction class​

The only one method available to use this functionality calling from the KFunction class is:

  • cardinality(KColumn kColumnArray): Receives a KColumn or a KTableColumn which will be supplied to the CARDINALITY function.

To use this way, you need to import the static functions as follows:

import static com.myzlab.k.KFunction.*;

Example​

Java code:

k
.select(
    cardinality(arrayAgg(APP_USER.EMAIL)),
    APP_USER.CREATED_AT.cast(date())
)
.from(APP_USER)
.groupBy(APP_USER.CREATED_AT.cast(date()))
.multiple();

SQL generated:

SELECT
    CARDINALITY(ARRAY_AGG(au.email)),
    CAST(au.created_at AS DATE)
FROM app_user au
GROUP BY CAST(au.created_at AS DATE)

Parameters:

  • None