> and this relates to the usage of ICU functions.
>
>

FB seems to set collation strength properly only where it relates to unique index.

>

Otherwise the strength is left default, i.e. equivalent of collate unicode, for unicode_ci and unicode_ci_ai.

>

This is my guess after tested and observed many cases.

>
>

If a sorting was ordered by a single column with collate UNICODE,

>

the result could be shared with collate UNICODE_CI or UNICODE_CI_AI.

>

But when it comes to ordering by multiple columns, it should be a different story.

>
>

Is there anyone who can check the relating source code?

>

ICU's collation strength must be set as follows to make sort key according to the field's collate property:

>

default(unicode), primary(unicode_ci_ai) or secondary(unicode_ci)

  Feel free to discuss it at fb-devel mailing list (https://sourceforge.net/projects/firebird/lists/firebird-devel)

Regards,

Vlad