The models we’ve created will now need to be populated with the data they’re intended to contain.
The goal for this lesson: To learn how to insert new data into the database models.
How do you add data to a table? The sql INSERT
statement provides the
functionality for this:
insert into streets (name) values ('High street');
A couple of things to note:
streets
), you list the column names that you
will be populating (in this case only the name
column).values
keyword, place the list of field values.id
column; this
is because it is a sequence and will be auto-generated.id
, you may cause serious problems with
the integrity of your database.You should see INSERT 0 1
if it is successful.
You can see the result of your insert action by selecting all the data in the table:
select * from streets;
Result:
select * from streets;
id | name
----+-------------
1 | High street
(1 row)
Use the INSERT
command to add a new street to the streets
table.
Try to add a person object to the people
table with the following details:
Name: Joe Smith
House Number: 55
Street: Main Street
Phone: 072 882 33 21
Note
Recall that in this example, we defined phone numbers as strings, not integers.
At this point, you should have an error report if you try to do this without
first creating a record for Main Street in the streets
table.
You should have also noticed that:
- You can’t add the street using its name
- You can’t add a street using a street
id
before first creating the street record on the streets table
Remember that our two tables are linked via a Primary/Foreign Key pair. This means that no valid person can be created without there also being a valid corresponding street record.
Using the above knowledge, add the new person to the database.
We have already shown you the syntax for selecting records. Let’s look at a few more examples:
select name from streets;
select * from streets;
select * from streets where name='Main Road';
In later sessions we will go into more detail on how to select and filter data.
What if you want to make a change to some existing data? For example, a street name is changed:
update streets set name='New Main Road' where name='Main Road';
Be very careful using such update statements - if more than one record matches
your WHERE
clause, they will all be updated!
A better solution is to use the primary key of the table to reference the record to be changed:
update streets set name='New Main Road' where id=2;
It should return UPDATE 1
.
Note
the WHERE
statement criteria are case sensitive Main
Road
is not the same as Main road
In order to delete an object from a table, use the DELETE
command:
delete from people where name = 'Joe Smith';
Let’s look at our people table now:
address=# select * from people;
id | name | house_no | street_id | phone_no
----+------+----------+-----------+----------
(0 rows)
Use the skills you have learned to add some new friends to your database:
name | house_no | street_id | phone_no
-----------------+----------+-----------+--------------
Joe Bloggs | 3 | 2 | 072 887 23 45
Jane Smith | 55 | 3 | 072 837 33 35
Roger Jones | 33 | 1 | 072 832 31 38
Sally Norman | 83 | 1 | 072 932 31 32
Now you know how to add new data to the existing models you created previously. Remember that if you want to add new kinds of data, you may want to modify and/or create new models to contain that data.
Now that you’ve added some data, you’ll learn how to use queries to access this data in various ways.