Ciao,
As much as I know, query content is on roadmap but not yet implemented, i.e., for now dataview queries are limited to data (via yaml frontmatter, inline-fields, implicit metadata).
By your explanation, I deduce you are trying query the content. If not, if is a value in a field like riassunto: Parliamo di storia della sperimentazione, then you can write:
WHERE containsword(riassunto, "storia")
What’s the difference between contains and containsword?
From what I understand so far, contains checks all elements (characters) in the value, with no distinction if is a word or just some characters put together (in your example you can check ‘toria’ and dataview found it in “Parliamo di storia della sperimentazione”).
But containsword seems to be more accurate and looks for case-insensitive precise word matches in a sentence (in your example you can write containsword(riassunto, "parliamo")).
Solo un’altra osservazione.
When you find in the documentation expressions like contains(file, "ctime") = true the = true isn’t to be placed in the query, is just to explain what the function does - in this case is a filter to dataview evaluate if the clause <contains(file, “ctime”)> is true (if not, dataview didn’t yields/shows the pages).
Tornando al punto di partenza.
If you want to filter/check the content, for now I think that is not possible with dataview (maybe with dataviewjs… but I don’t have knowledge in java).