db save fail does not work

db save, where condition works and update
if where condition fails it does not save it is supposed to be but it does not read inside of fails condition of db save
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it says your record is saved succesfully
but it is not

That's not what that fail event is for. It's for
a) the database action encounters an error or
b) you put a /+ after a condition, and the data isn't there. E.g. field:{data:fieldname}/+ and there's no fieldname data.
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What's happening, is that it's successfully updating all the records meeting your condition - it just so happens that none of them do. Sounds like what you need to do is put a read data action first, and check if the record you want exists.

right thanks
i put event switcher and works
but i donot understand still
field:{data:fieldname}/+
what is this for?

I told you what it's for. Have another look.