Joining Tables - MACROMEDIA DREAMWEAVER MX 2004-USING DREAMWEAVER Use Manual

Joining tables

You can use a single statement to retrieve data from more than one table in the database.
SELECT
The statement joins the tables and returns a single recordset containing selected data from
each table.
For example, a company database might contain one table with personal data about employees
and another table with data about the company's departments. If you want to build an employee
directory that displays an employee's name, phone number, and department, you must retrieve
information from the two tables simultaneously.
To do this, create a join specifying all the tables to include and how the tables are related to each
other. Here's an example:
SELECT FIRSTNAME, LASTNAME, PHONE, DEPTNAME
FROM EMPLOYEES, DEPARTMENTS
WHERE EMPLOYEES.DEPT_ID = DEPARTMENTS.DEPT_ID
Note: Use dot notation to identify the columns more precisely. For example,
EMPLOYEES.DEPT_ID refers to the DEPT_ID column in the EMPLOYEES table.
The first line specifies the columns to retrieve. The first three columns—FIRSTNAME,
LASTNAME, PHONE—exist in the EMPLOYEES table, while the fourth column—
DEPTNAME—exists only in the DEPARTMENTS table.
The second line specifies the two tables from which to retrieve data, EMPLOYEES
and DEPARTMENTS.
The final line specifies the records to join and retrieve from the two tables. Each table has a
column called DEPT_ID. (In the DEPARTMENTS table, the column is the primary key. For
more information, see "Defining relationships between the tables" on page 745.) The
WHERE
clause compares the value of DEPT_ID in one table to the value of DEPT_ID in the other table.
When a match is found, all the fields of the record in the EMPLOYEES table are joined with all
the fields of the record in the DEPARTMENTS table. Next, the combined data is filtered to
create a new record made up of a FIRSTNAME, LASTNAME, PHONE, and DEPTNAME
column. Finally, the new record is added to the recordset.
Using slightly different join syntax may be preferable in some database systems. For example, the
following SQL statement uses the SQL keywords to achieve the same results as
INNER JOIN...ON
the previous example:
SELECT FIRSTNAME, LASTNAME, PHONE, DEPTNAME
FROM EMPLOYEES INNER JOIN DEPARTMENTS
ON EMPLOYEES.DEPT_ID = DEPARTMENTS.DEPT_ID
Consult your database system's documentation to determine which join syntax you should use.
Related topics
•
"Defining relationships between the tables" on page 745
Joining tables 759