select * into NEWTABLE from OLDTABLE where 1=0

       SELECT TOP (50) PERCENT * INTO NewTable1 
       FROM MyOldTable1 
       
       SELECT * INTO NewTable2 
       FROM MyOldTable1 ot1
       WHERE NOT EXISTS (SELECT 1 
                         FROM NewTable1 nt1 
                         WHERE nt1.[UniqueIdColumn(s)] = ot1.[UniqueIdColumn(s)])
       
       SELECT * INTO NewTable3 
       FROM MyOldTable2

ALTER Table1 add ColA type1 columnConstraints1, ColB type2 columnConstraints2;
ALTER Table2 add ColC type 3 columnConstraints3;