Update (crUd) using Perl and DBD::ORACLE

In this post, we’re going to take a look at the U in CRUD: Update.

We use the DBD::Oracle driver to update some data in the database tables, using the connection object created in the Initial Setup section of the first post in this series.


Helper Function

My helper function get_all_rows() encapsulates a select statement used to verify that the updates worked. The select functionality is covered in the R part of this series, so I won’t go into the details here.

Add this function to the top of your file.

Resetting the data

To keep the examples clean and precise, I will reset the data at times.

Create a new file called reset_data.perl with the following code and then run it whenever you would like to reset the data. (Notice this version adds pet data not included in other sections.)

Boilerplate template

The template we will be using is:

For each exercise, replace the “# Your code here” line with your code.

Simple update

We will perform a simple update that modifies a single record in the lcs_people table.  These are the steps performed in the code snippet below.

  • Prepare a SQL UPDATE statement, changing age to 31 for the record with an id of 1.
  • Bind the age and id values.  (See the R part of this series for an explanation of bind variables.)
  • Execute the statement.
When I run this code in my Perl session, I see:

Extra Fun 1

Update Bob’s notes to ‘I like cats’ .

Your results should be:


Reset the data

Now is a good time to run reset_data.perl.

Boilerplate change

Change the boilerplate get_all_rows statements to get pet data.

Make sure your where clause is specific

In the above example, notice that we used the id column in our where clause.  For our data set, id is the primary key.  You do not always have to use a primary key, but you should make sure you only update the rows you intend to.

Next, let’s look at updating multiple rows.   We’ll have Bob give his dog Duke to Kim.

  • Prepare a SQL UPDATE statement, changing owner to 2 for the record with an owner of 1 and a type of ‘dog’.
  • Bind the newOwner, oldOwner and type values.
  • Execute the statement.
When I run this code in my Perl session, I see:

In our example we only used owner and type, assuming that Bob only had one dog, Duke, as it is in our original data.  With the new reset data function, we added a second dog, Buster.  This example is intended to demonstrate what may happen when multiple users are working with the same data set.

In our data, the only unique identifier for lcs_pets is id.  Bob may have two dogs, or even two dogs named Duke.  Make sure if you intend to change a specific row you use a unique identifier.

It also helps to…

Verify the number of affected rows

Now let’s give Buster back to Bob.  This time we will use the unique id column and we will print out the number of rows affected using $sth->rows.

  • Prepare a SQL UPDATE statement.
  • Bind the newOwner to 1 and id to 6.
  • Execute the statement.
  • Get the number of changed rows.
  • Print the number of changed rows.
When I run this code in my Perl session, I see:

$sth->rows will show you the number of rows affected for insert, update and delete statements and -1 for a select statement.

Extra Fun 2

Give all birds to Kim that she doesn’t already have and print the number of affected rows .

Your results should be:


Some other things you could try
  • Change multiple column values
  • Perform an update that changes all rows, if the row count is greater than 2, rollback the change

Series sections

Initial Setup
Create records
Retrieve records
Update records
Delete records

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