Question

The PATIENTS and DOCTORS tables contain these columns:

PATIENTS
PATIENT_ID NUMBER(9)
LAST_NAME VARCHAR2 (20)
FIRST_NAME VARCHAR2 (20)
DOCTORS
DOCTOR_ID NUMBER(9)
LAST_NAME VARCHAR2 (20)
FIRST_NAME VARCHAR2 (20)
You issue this statement:
SELECT patient_id, doctor_id
FROM patients, doctors;
Which result will this statement provide?
a.A report containing all possible combinations of the PATIENT_ID and DOCTOR_ID values
b.A report containing each patient's id value and his doctor's id value
c.A report with NO duplicate PATIENT_ID or DOCTOR_ID values
d.A syntax error

Answer 1

The SQL statement will generate a report with all possible combinations of PATIENT_ID and DOCTOR_ID due to the lack of a JOIN clause, resulting in a Cartesian product.

Step-by-step explanation:

The statement issued, SELECT patient_id, doctor_id FROM patients, doctors;, will produce a report containing all possible combinations of the PATIENT_ID and DOCTOR_ID values. This is because the query does not specify how the two tables should be joined or related, so it creates a Cartesian product, meaning every row from the PATIENTS table is paired with every row from the DOCTORS table. There is no restriction placed on the data, and there is no JOIN clause used to combine the two tables based on a relationship between them.