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There is one table in HTGDEV user.The name is 'RTS'.
when I am using select * from Tab where upper(tname)='RTS';
Then I will get the one record.
But when I am using select * from RTS;
Then I got the message 'table or view does not exist'
That code doesn't mean much of anything since the queries use two different tables. We have no idea what the 'Tab' table is or what is contained in the 'tname' column.
We also have no idea what user you are connected as or whether that user has been granted select privileges on any RTS table.
Repost your question in the proper forum.