How to know if user choose to show full post or excerpt?

Show summary or full textx for feeds

That option refers to show excerpt on rss/atom feeds, not to normal frontend archives.

You can get that value using

get_option( 'rss_use_excerpt' );

That is 1 if user choose “Summary”, 0 if user choose “Full text”.

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)