- More to come
ksqlDB Table Functions¶
A table function is a function that returns a set of zero or more rows. Contrast this to a scalar function, which returns a single value.
Table functions are analogous to the
FlatMap operation commonly found in
functional programming or stream processing frameworks such as
Table functions are used in the SELECT clause of a query. They cause the query to output potentially more than one row for each input value.
The current implementation of table functions only allows a single column to be returned. This column can be any valid SQL type.
Here's an example of the
EXPLODE built-in table function, which takes an
ARRAY and outputs one value for each element of the array:
The following stream:
1 2 3 4 5 6 7 8
When scalar values are mixed with table function return values in a SELECT
clause, the scalar values, like
sensor_id in the previous example, are
copied for each value returned from the table function.
You can also use multiple table functions in a SELECT clause. In this
situation, the results of the table functions are "zipped" together. The total
number of rows returned is equal to the greatest number of values returned from
any of the table functions. If some of the functions return fewer rows than
others, the missing values are replaced with
Here's an example that illustrates using multiple table functions in a SELECT clause.
With the following input data:
And the following stream:
1 2 3 4 5 6 7 8 9
This function takes an Array and outputs one value for each of the elements of the array. The output values have the same type as the array elements.