I don't know what I am doing wrong .
UPDATE acid_xyz SET hire_date = (select from_date from acid_abc where acid_xyz.eid = acid_abc.eid);
Yes I know but where clause in your select query doesn't make sense. Try to run just the select clause and see what you get.
Per apache hive documentation subquery for update is not supported
Also note that support for a JOIN clause in the update statement is not available. See this HCC article for more information and a link to the Hive JIRA requesting support for a MERGE statement. https://community.hortonworks.com/questions/11652/how-to-update-hive-row-with-join.html