I remember the many forums back then in the 2000’s. They had a great advanced search function.
What a good search function needs:
To choose the forum’s category or subcategory. But it still should be possible to search in all categories like it’s the case right now.
To choose if the keyword is only included in the threads title or within the posted text. If you can distinguish between the text of only the opening post versus all posts – even better.
Minus keywords (by setting a minus sign (-keyword) before the keyword). They were the standard everywhere, but vanish more and more. It’s hard to comprehend: Minus keywords are so important to give the possibility to exclude unneeded search results.
To put several keywords in quotation marks ("keyword keyword") in order to only show threads/posts with exactly these keywords in exactly this order.
Not that important but still useful:
To set time limits from a certain day-month-year until day-month-year of the threads opening date.
To allow a asterisk (keyw*) as a place holder for incomplete keywords.
To set a selection of keywords, where only one of them has to be found (or-function) by putting the keywords into parentheses: (keyword keyword keyword)
Why an advanced search function is important:
For users to find quickly what they are looking for.
To avoid new threads are opened with the same questions again and again. It's much more user-friendly if all answers can be bundled into one thread than being split up into many threads with the same questions/matters.
To avoid that threads are faded into oblivion too fast.
