Created attachment 162004 [details]
Screenshot of the error, which destroys connection to internal Firebird

Have found the reason in the code.
If I write this:

SELECT "a"."Datum" FROM "Ansicht_Datum_lfdNr" AS "a" WHERE "a"."Datum" BETWEEN '2020-01-01' AND '2020-12-31'

Firebird database will disconnect

and if I get the same with
SELECT "a"."Datum" FROM "Ansicht_Datum_lfdNr" AS "a" WHERE "a"."Datum" >= '2020-01-01' AND "a"."Datum" <= '2020-12-31'

Firebird will work as expected. But Firebird should know what "BETWEEN" is. It is content of the docs of Firebird - and the alternative I wrote down is shown there also as the possibility to get the same result.

If I try this with 

Version : 6.4.4.2
Build ID : 3d775be2011f3886db32dfd395a6a6d1ca2630ff
Threads CPU : 8; OS : Mac OS X 10.15.4; UI Render : par défaut; VCL: osx; 
Locale : fr-FR (fr_FR.UTF-8); Langue IHM : fr-FR
Calc: threaded

I see the tables list slowly disappearing as I choose a table from the list after clearing the preceding error message, until LO finally crashes.

Confirming.

Created attachment 167312 [details]
bt with debug symbols

On pc Debian x86-64 with master sources updated today, I reproduced the crash by launching LO and just launch SQL with:

SELECT "a"."Datum" FROM "Ansicht_Datum_lfdNr" AS "a" WHERE "a"."Datum" BETWEEN '2020-01-01' AND '2020-12-31'

Just for curiosity, do you reproduce an error or kind of crash by testing directly on Firebird if you create the same tables and view?

I gave a try with:
SELECT "a"."Startdatum" FROM "Reservierung" AS "a" WHERE "a"."Startdatum" BETWEEN '2020-01-01' AND '2020-12-31'

So the pb seems to be the use of "BETWEEN" on a view.

(In reply to Julien Nabet from comment #5)
> I gave a try with:
> SELECT "a"."Startdatum" FROM "Reservierung" AS "a" WHERE "a"."Startdatum"
> BETWEEN '2020-01-01' AND '2020-12-31'
> 
> So the pb seems to be the use of "BETWEEN" on a view.

Sorry, forgot to say it worked with quoted query. (still by using Tools/SQL...)

I have tried it with the same database as external file. Same buggy behavior.

Then I tried to import the data from the internal file to a Firebird ODBC connected database. It is impossible to get both databases open the same time in LO. So I couldn't copy the content.

Then I copied the file to the server path of Firebird, but the user I have installed has no right to connect to the tables in the file. And another bug appeared: With LO 7.0.3.1 LO crashes immediately when I connect to Edit → Database → Properties

So I gave up to test if the query will work in a server-database of Firebird.

(In reply to Robert Großkopf from comment #7)
> ...
> So I gave up to test if the query will work in a server-database of Firebird.
I understand.
I tried with LO Debian package 7.0.3 and master sources, each time sub entries of Edit/Database (Properties..., Connection Type..., Advanced Settings...) are disabled.

(In reply to Julien Nabet from comment #8)
> (In reply to Robert Großkopf from comment #7)
> > ...
> > So I gave up to test if the query will work in a server-database of Firebird.
> I understand.
> I tried with LO Debian package 7.0.3 and master sources, each time sub
> entries of Edit/Database (Properties..., Connection Type..., Advanced
> Settings...) are disabled.

Ok it's disabled because I use embedded Firebird in LO and you were testing with LO + external server Firebird.

I don't reproduce this with master sources updated today.
First I thought it may be related to Firebird upgrade to 3.0.7 but then I tested again with LO Debian package 7.0.3, quite weirdly, I don't reproduce this.

About Database properties, it's been fixed from next release 7.0.4, see tdf#138240 (or daily master or daily 7.1 branch)

Couldn't reproduce the bug any more with LO 7.4.3.2 on OpenSUSE 15.3 I close this one as WORKSFORME.