select from and update into the same table

I have table (TEST) with columns (tid, title, subject). I need to select first 30 chars of (subject) and update it in to its (title) column as follows. When I tried the following, it says SQL command not properly开发者_开发技巧 ended. Any idea?

update a set a.title = substr(b.subject, 0, 30) from trkowner.test a join trkowner.test b on a.tid = b.tid;

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You don't need join in this case. Just perform:

update trkowner.test set title = substr(subject, 0, 30)