SPECIAL IMPLEMENTATION CONSIDERATIONS - Database Design and Development: An Essential Guide for IT Professionals - page 399

FROM BILLING
WHERE ServiceCode = 'SCAN') )
6. Obtain a list of all billings including those patients for whom no billings have
been done until now.
SELECT BILLING.PatientNo, PatientName, BilledAmount
FROM BILLING, PATIENT
WHERE BILLING.PatientNo = PATIENT.PatientNo
UNION
SELECT PatientNo, PatientName, 0
FROM PATIENT
WHERE PatientNo NOT IN
(SELECT PatientNo
FROM BILLING)

Summary of SQL Query Components

Having reviewed various types of SQL queries, let us summarize the different query
components. Figure 13-12 provides a summary of the main clauses, operators, and
built-in functions that are part of typical SQL queries.

Database Access from Application Program

The queries discussed in the previous subsection illustrate one method of using
SQL. We have covered the interactive use of SQL. To obtain the desired results
from the database, you write SQL code in the database environment. The com-
mercial database systems support SQL and execute the SQL statements interac-
tively. The end of the SQL code, usually signified by a semi-colon (;), triggers the

SELECT

GROUP BY
HAVING

ORDER BY

Retrieval

SUM
AVG
COUNT
DISTINCT
MIN
MAX

S Q L

Update

INSERT
DELETE
UPDATE

Figure 13-12 SQL query and manipulation components.