Timestamp to Big Query Datetime

[KHK]

Hi 

My Source table is Big Query Table and Target table is Big Query Table.

I have created MV and sent to Data Destination getting below error.

Big Query Table DateTime Format is as below.

I have written formula forEXT_LAST_UPDATE DATE as 

COALESCE(

  to_timestamp(EXT_LAST_UPDATE_DATE, 'yyyy-MM-dd HH:mm:ss'),

  to_timestamp(EXT_LAST_UPDATE_DATE, 'yy-MM-dd HH:mm:ss')

) AS EXT_LAST_UPDATE_DATE

Please let me know how to convert Timestamp to Datetime.