Tip: Using isql-fb / isql with readline in Debian/Ubuntu instead of libedit

Seems that readline does have utf-8 support and can be used for inserting/selecting accented chars
Check if libedit is used instead of readline

ldd /usr/bin/isql-fb | grep libedit
libedit.so.2 => /usr/lib/libedit.so.2 (0x00007f3dcbd7b000)

export LD_PRELOAD=/lib/libreadline.so.6

check if is preloaded

ldd /usr/bin/isql-fb | grep readline
/lib/libreadline.so.6 (0x00007fc661d22000)

Then use isql-fb as usual

SQL> select * from employee where first_name = ‘ő’