[DUG] Using Queries

[Bevan Edwards]

Hi Adrian,

I have used TQuery objects to read data from databases (sometimes 
complex, sometimes simple), and then other TQuery objects to perform 
update/insert/delete operations.

The fact that you "can" perform update/insert/delete on a (presumably 
simple) TQuery seems like a side-effect of how it is implemented, rather 
than an acceptable/intended approach.

In my view, a SELECT query is for read-only purposes and should not then 
be used to directly update the database.
If you wanted to update the database like that, you would use a TTable 
rather than a TQuery.
Again, that's probably better suited to file-based databases (like 
Paradox and MS Access) rather than SQL-based databases.

That's my two cents worth anyway.

Regards,

Bevan


On 13/06/2022 10:05 am, Adrian Williams wrote:
> Hi all
>
> I wonder if someone could clarify something regarding Queries.
>
> I understand that if you run a query on a table it returns a  subset or
> snapshot of data from the table based on the SQL statement supplied. (In
> my Paradox days, a query created an 'ANSWER' table that could be
> navigated as a table, but was separate from the original data).
>
> What I have discovered (more by accident), is that if you edit records
> in the query data and call  the query's POST method it will post the
> changes back to original table. Also by using the APPEND and INSERT
> methods on the query, you can create new records in the base table. What
> I have been able to ascertain is that the database engine seamlessly
> creates the SQL code to run UPDATE and INSERT statements to amend the
> original table in the background.
>
> My question is: Is this a 'proper' and acceptable way of updating a
> table by modifying the Query data? Or is this fraught with danger and
> bad practice?
>
> Appreciate any comments on this.
>
> Regards
> Adrian Williams
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