A database's primary purpose is to store and help extract information you are looking for. Unlike databases written on a paper sheets, Kexi database allows you to specify more search criteria. Results are returend faster even for large data sets. All this is a power of databases, however to be able to perform efffective queries in your database, you need to learn how to tell the database what you are looking for.
With database queries you can limit data coming from a table to a predefined set of rows and columns as well as dynamically join data coming from multiple tables.
To see how queries work in practice you will create a contacts
query joining data from two tables: persons
and
phone_numbers
(designed in
chapter 3.1i
and filled with data in
chapter 3.2
).
Create a new empty query by selecting -> from the menubar. The design window will appear. The window is split into two areas: query relationships at the top and query columns below.
Select the table persons
in the drop down list Table:
located at the top of the window and click the button. A graphical
representation of the table will appear in the relations area. Do the same for the
phone_numbers
table to insert it too, as in the figure below.
Add query relationship using mouse drag & drop technique: click the field
id
in the table persons
table, drag it
and drop into the person
field of the phone_numbers
table. This will join both fields by creating a new relationship.
Double-click the name
field in the persons
table, to add the field as a query column. In a similar way,
add surname
, street
, house_number
,
city
fields from the persons
table and
phone
from the phone_numbers
table.
Query design is now ready for testing. Click the button on the toolbar, to switch from design to viewing the data provided as query results.
Save the query design for later use by clicking the
button on the toolbar. You can also use
->
from the menubar or press the Ctrl+S
keys. Because the query design has not been saved yet, you will be asked to
specify a name for it. Enter Contacts
text in the
caption field and click the button.
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