CDS Table function example to determine number of ... - SAP Community

Hi there,

currently I am on an example for a CDS table function to determine the number of records of a specific attribute.
Note: This is just an example for me to unterstand the functionality of such a CDS table function.
Please do not suggest different solutions like "for your use case you don't need a table function etc."
My use case is simplified!

Unfortunately, I don't get the solution on my own at the moment. Some parts I don't understand yet... 

This is my use case:

Given database table:

ID

id_1

id_1

id_1

id_2

id_2

id_3

Using the table function I want to get a result of the following structure:

ID	number
id_1	3
id_2	2
id_3	1

So the number column shall only contain the count of occurrences of each ID.

This is what I got in coding yet:

CDS Table function:

@EndUserText.label: 'Test'
@ClientDependent: false
define table function MY_TABLE_FUNCTION
returns {
id : z_id;
number : z_number;
}
implemented by method zcl_table_function=>read;

CLASS zcl_table_function DEFINITION
PUBLIC
FINAL
CREATE PUBLIC.

PUBLIC SECTION.
  INTERFACES if_amdp_marker_hdb.
  
  CLASS-METHODS read FOR TABLE FUNCTION my_table_function.
ENDCLASS.

CLASS zcl_table_function IMPLEMENTATION.
  METHOD read BY DATABASE FUNCTION
              FOR HDB
              LANGUAGE SQLSCRIPT
              OPTIONS READ-ONLY
              USING my_table.

  return select my_table.id from my_table as my_table;

ENDMETHOD.
ENDCLASS.

CLASS zcl_table_function_call DEFINITION
PUBLIC
FINAL
CREATE PUBLIC.

PUBLIC SECTION.
  METHODS call.
ENDCLASS.

CLASS zcl_table_function_call IMPLEMENTATION.
  METHOD call.
    SELECT * FROM my_table_function( )
      INTO TABLE (result).
  ENDMETHOD.
ENDCLASS.