[Koha] Keyword search in Koha

[Michael Kuhn]

Hi

Lately I stumbled upon some strange behaviour of the keyword search in 
Koha. In our library we are using an unchanged Zebra configuration as 
coming with Koha 20.11.00.

The Koha manual describes the keyword search in the following chapter: 
https://koha-community.org/manual/20.11/en/html/searching.html#basic-searching

1. The manual says: "When a single word is entered, a keyword search is 
performed. You can check this out by typing one word into the form and 
note the number of results located. Then, repeat the search with a minor 
change. In front of the search word, type ‘kw=’ followed by the same 
search term. The results will be identical." I did check this out and 
the result was NOT identical. Why is that so?

The following searches produce a difference of four results:

Search for: biology
* URL: .../search.pl?q=biology
* 5939 results

Search for: kw=biology
* URL: .../search.pl?q=kw%3Dbiology
* 5935 results

The following searches produce a difference of 49 results:

Search for: life
* URL: .../search.pl?q=life
* 837 results

Search for: kw=life
* URL: .../search.pl?q=kw%3Dbiology
* 788 results

2. The manual also says: "When you have more than one word in the search 
box, Koha will still do a keyword search, but a bit differently. Each 
word will be searched on its own, then the Boolean connector ‘and’ will 
narrow your search to those items with all words contained in matching 
records." I did check this out and it does not seem to be true - if I 
just enter two words (biology life) I get 37 more results than when I'm 
using the boolean operator AND. What is the explanation for this?

Search for: biology life
* URL: .../search.pl?q=biology+life
* 521 results

Search for: biology AND life
* URL: .../search.pl?q=biology+AND+life
* 484 results

Search for: kw=biology AND kw=life
* URL: .../search.pl?q=kw%3Dbiology+AND+kw%3Dlife
* 484 results

Especially I'm stunned because the first search does not seem to be 
using the OR operator but still produces considerably more results than 
the searches using the AND operator.

3. Is there maybe some undocumented use of using wildcards going on if 
one is not using a search prefix?

Best wishes: Michael
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