Hello Angel,
First point, Count(*) is of type BIGINT hence there is a datatype mismatch with INTEGER
try the following....
CREATE TABLE TESTTABLE AS (SELECT count(*) "COUNT" from "AADI"."TMP_REALDATA")
Now, view the table definition.
Second question,
Try CE_VERTICAL_UNION (http://help.sap.com/hana/SAP_HANA_SQL_Script_Reference_en.pdf) pg 103
But it is not advisable to mix SQL and CE functions, so more information on your use case on why you want to add a column would be helpful...
Warm regards
aadi