While it is true that COALESCE is equivalent to ISNULL, writing a completely equivalent query is not quite that easy. Teradata does not allow "select top n" in a subquery.
Even conceptually, "select top 1" in a subquery is nonsensical in Teradata since it presumes some ordering of the result set. If you can explain what result you expect from that subquery, it might be possible to suggest an equivalent query.
Strange query: - if cp2_eff_dt/EFF_DT is actually a datetime in SQL Server, then why it's coalesced with an integer zero?
- it's all rows from CAP_SAC_CP211 or none, but it's kind of random, because TOP without order by is non-deterministic in SQL Server, too. If this actually returned the maximum date, then it was the right clustered index and luck.
Without TOP this is similar: SELECT * FROM CAP_SAC_CP211 WHERE EXISTS (select * from CAP_SAC_CP211 where cp2_eff_dt > coalesce (SELECT MAX(EFF_DT) FROM CORPT_PLCY_CR_WKLY_SNAP_DATA), date '0001-01-01') )