I modified example 1 so that the syntax is accepted by all vendors that I tried. It turns out that the only DBMS of the tested ones that reject the scenario is Db2 DB<>Fiddle:

MariaDB 10.2, 10.3 Yes
MySQL 5.6, 5.7, 8.0 Yes
Postgres 11 Yes

Oracle 11g release 2, 18 Yes
SQLServer 2017 Yes
Db2 V11 No

Note that the foreign keys have to be slightly modified for Oracle and SQLServer. See links provided by Dinesh Kumar

Oracle SQLServer

I skimmed through 7IWD2-02-Foundation-2011-12.pdf which can be download from:

http://www.wiscorp.com/sql20nn.zip

but I did not find anything mentioned regarding this.

To me, it seems as if Db2 behave sanely in this regard, but that's just my opinion.

I modified example 1 so that the syntax is accepted by all vendors that I tried. It turns out that the only DBMS of the tested ones that reject the scenario is Db2 DB<>Fiddle:

MariaDB 10.2, 10.3 Yes
MySQL 5.6, 5.7, 8.0 Yes
Postgres 11 Yes

Oracle 11g release 2, 18 Yes
SQLServer 2017 Yes
Db2 V11 No

Note that the foreign keys have to be slightly modified for Oracle and SQLServer. See links provided by Dinesh Kumar

Oracle SQLServer

Db2 throws an exception like:

SQL20255N FOREIGN KEY .. is not valid because it would cause a descendent table ... to be delete-connected to its ancestor table ... through multiple relationships with conflicting delete rules. The conflict is between the delete rules of constraints ... and ... on the descendent table. Reason code = "3". SQLSTATE=42915 SQLCODE=-20255

I skimmed through 7IWD2-02-Foundation-2011-12.pdf which can be download from:

http://www.wiscorp.com/sql20nn.zip

but I did not find anything mentioned regarding this.

To me, it seems as if Db2 behave sanely in this regard, but that's just my opinion.

I modified example 1 so that the syntax is accepted by all vendors that I tried. The open-source DBMS all accept the conflicting f.k. in D, whereas none of the commercial vendors did DB<>Fiddle:

MariaDB 10.2, 10.3 Yes
MySQL 5.6, 5.7, 8.0 Yes
Postgres 11 Yes

Oracle 11g release 2, 18 No
SQLServer 2017 No
Db2 V11 No

I skimmed through 7IWD2-02-Foundation-2011-12.pdf which can be download from:

http://www.wiscorp.com/sql20nn.zip

but I did not find anything mentioned regarding this.

To me, it seems as if Db2, Oracle and SQL-server behave sanely in this regard, but that's just my opinion.

I modified example 1 so that the syntax is accepted by all vendors that I tried. It turns out that the only DBMS of the tested ones that reject the scenario is Db2 DB<>Fiddle:

MariaDB 10.2, 10.3 Yes
MySQL 5.6, 5.7, 8.0 Yes
Postgres 11 Yes

Oracle 11g release 2, 18 Yes
SQLServer 2017 Yes
Db2 V11 No

Note that the foreign keys have to be slightly modified for Oracle and SQLServer. See links provided by Dinesh Kumar

Oracle SQLServer

I skimmed through 7IWD2-02-Foundation-2011-12.pdf which can be download from:

http://www.wiscorp.com/sql20nn.zip

but I did not find anything mentioned regarding this.

To me, it seems as if Db2 behave sanely in this regard, but that's just my opinion.