Vertica Partition Function Usage Issue

 I have a doubt regarding some internal Vertica functions.

 - in the latest Vertica version the copy_partition_to_table has been implement and i find this very usefull.

COPY_PARTITIONS_TO_TABLE (
    '[[db-name.]schema.]source-table',
    'min-range-value',
    'max-range-value', 
    '[[db-name.]schema.]target-table'
)

Also we have  swap_partition_... which is an older function .

SWAP_PARTITIONS_BETWEEN_TABLES (
    '[[db-name.]schema.]staging-table',
    'min_range_value',
    'max_range_value', 
    '[[db-name.]schema.]target-table'
)

Now here is my doubt !:

 Why would in one we should use integer values as an input and in other it has to be a string .

To give you an example as my use case:

-- i am moving data from staging to prod once this is clean.

SELECT SWAP_PARTITIONS_BETWEEN_TABLES ( 
'$$Vertica_Stg_Schema.Fact', CAST(TO_CHAR(ADD_MONTHS(SYSDATE,-1),'YYYYMM') AS INTEGER), 
CAST(TO_CHAR(SYSDATE,'YYYYMM') AS INTEGER), 
'$$Vertica_Prd_Schema.Fact'
) ;

-- it works great , no isues so far .

Notice the cast i issue to make it a INTEGER.

Now i wanna use the copy_partition_to_table for my work using the same dynamic partition key generation.

SELECT /*+ LABEL(copy_part) */ COPY_PARTITIONS_TO_TABLE('
prod.Fact,
CAST(TO_CHAR(ADD_MONTHS(SYSDATE,-26),'YYYYMM')AS INTEGER),
CAST(TO_CHAR(SYSDATE,'YYYYMM')AS INTEGER) ,
'staging.Fact_to_bkp');

I get this error :

 ERROR: Function COPY_PARTITIONS_TO_TABLE(unknown, int, int, 
unknown) does not exist, or permission is denied for 
COPY_PARTITIONS_TO_TABLE(unknown, int, int, unknown)

This is strange !? Right 

So the working SQL is :

SELECT /*+ LABEL(copy_part) */ COPY_PARTITIONS_TO_TABLE(
'prod.Fact',
TO_CHAR(ADD_MONTHS(SYSDATE,-26),'YYYYMM'),
TO_CHAR(SYSDATE,'YYYYMM') ,
'staging.FactScript_to_bkp'
);

Solution :

- pass the partition keys as String values. 

 What is the reason befind makeing them different one takes int and another takes string ?

Just out of curiosity  

Thanks all HP Vertica Eng Team.