Database Reference
In-Depth Information
■
Make sure every table has a primary key (refer to Chapter 15, “Joining
Tables,” if you have forgotten what this is) and use it as the
WHERE
clause whenever possible. (You may specify individual primary keys,
multiple values, or value ranges.)
■
Before you use a
WHERE
clause with an
UPDATE
or a
DELETE
, first test
it with a
SELECT
to make sure it is filtering the right records—it is far
too easy to write incorrect
WHERE
clauses.
■
Use database enforced referential integrity (refer to Chapter 15 for this
one, too) so MariaDB does not allow the deletion of rows that have
data in other tables related to them.
Caution
Use with Caution The bottom line is that MariaDB has no Undo button. Be very careful
using
UPDATE
and
DELETE
, or you might find yourself updating and deleting the wrong
data.
In this chapter, you learned how to use the
UPDATE
and
DELETE
statements
to manipulate the data in your tables. You learned the syntax for each of these
statements, as well as the inherent dangers they expose. You also learned why
WHERE
clauses are so
important in
UPDATE
and
DELETE
statements, and you
were given guidelines to follow to help ensure that data does not get damaged
inadvertently.
