Processing Data
Queries that Change Data
Access queries are
used to process data from a table (or tables.)
“Select” queries simply
display specific data from the underlying tables
possibly sorting that data in a new order and even filtering some of it out.
Other queries are
not quite so harmless.
I say “harmless”
because you can’t do much damage to the underlying data if you only display it.
Even filtering and sorting may seem to change the data, but it doesn’t.
When using criteria
to filter out some rows,
the “missing” data is still in the table, just not in the query’s results.
However, “action”
queries are designed to modify data in some way.
Each kind of “action”
query modifies data in a different way,
such as changing values, moving data from one table to another,
or deleting existing values from a table.
Here is the list you
have to choose from :
The
“Make Table” query is the only actual “harmless” query,
since this type copies data from one table to a brand new table,
and the only thing that is changed is the new table.
If
you mess it up, you can just make another new table, right ?
Once you run one
of the other “not so harmless” queries,
there is no going back. There is
usually no “Undo” key to save you.
These action queries
will typically warn you :
but if you don’t
heed the warning, you’re out of luck.
(That’s why we
make backups.)