how to delete lines in txt file which contains 2 or more specific characters

I have large txt files which i want to import to database. I need only one : on every line.If there is more :: these characters on line i want to delete that line. Any suggestions how to do it ?. I would like to use editors as notepad++ or something similar.

    it looks like this for example

fizol23@seznam.cz::1234::
yaehl005lhey@seznam.cz:dimayacyac
robjtim@seznam.cz:thatcher1
fchrismo49@seznam.cz:494949
melanie3850@seznam.cz:jacobbb:
trishmercado@seznam.cz:brooklyn

Solution

You can use lookarounds to do this.

^.*(?=:.*:).*$

This effectively says match everything from the start of the line ^.* to the end of the line .*$ where there are at least 2 colons on that line.

If you only want to match lines with specifically :: (no characters between them) then you can specify that in the lookaround ( ^.*(?=::).*$ ).

You can read more about lookarounds here: https://www.regular-expressions.info/lookaround.html.