Hi, Actually i am new to teradata. I you find any thing silly please ignore and clarify my doubt. Kindly let me know if more explanation is required.
1. CREATE Table Employee_Table12 AS
CREATE TABLE AS existing table copies all index definitions and table/column options (like FORMAT, NOT NULL or SET/MULTISET), while CREATE TABLE AS SELECT drops all those resetting everything to defaults.
When you do a SHOW TABLE you can easily see the differences.
You can change index definitions using both techniques, test it and do SHOW TABLE again