Re: SQL can select from this DDM (Distributed Data Managment) file

On 07-Oct-2010 16:40, elehti wrote:

DDM file AMSDTA/F0005, created 7 years ago in 2003, IS
viewable with STRSQL SELECT statements, but WHY?

None of our other DDM files are viewable in SQL.

<<SNIP>>

The device file [*FILE object-type] with the object attribute DDMF is the [optional] "implementation object" for the SQL ALIAS which need only be an entry in the catalog [much like the logical database file is the implementation object for the SQL INDEX]. A DDMFile which exists to implement the effect of the SQL statement CREATE ALIAS will *appear to* be accessible via the SQL for DML statements. However more accurately, the existence of that ALIAS name in the SQL catalog as a row in SYSTABLES with TABLE_TYPE='A', is what allows the SQL DML access; e.g. using the noted SELECT.

The following query result would confirm that, what appears to be a *LOCAL Distributed Data Management device file is instead, merely an implementation object for a SQL ALIAS:

SELECT *
FROM qsys2/systables
WHERE table_schema='AMSDTA'
and sys_tname= 'F0005'
and TABLE_TYPE='A'

While the *FILE object created with\for the CREATE ALIAS request may be changed [e.g. CHGDDMF] and then accessed also as a [local, or I believe also remote] DDM file, doing so is highly discouraged since there is no support for the effect, even though there is no code [yes] to prevent such actions. Because the *FILE object is merely an implementation object [which is subject to change], no dependence should be coded on its existence after a request to perform the CREATE ALIAS. That said, I have several times modified my ALIAS to function the same via RLA as it does via SQL; i.e. to point to the desired *LOCAL file.member as specified in the CREATE ALIAS.

Regards, Chuck