Database Programming - Study Guide Sections 3-4
Name ________________________________________________ Date ___________________
1.
Explain the joining of tables?
Sometimes data from more than one table is needed on the same report.
2.
What are a Cartesian Product and a CROSS JOIN, are there any differences?
A Cartesian Product and a CROSS JOIN merge the tables’ data into one big
report. Many rows and columns are displayed. The only difference is how the
FROM clause is written, a comma separating the tables for a Cartesian Product
and the actual words ‘CROSS JOIN’ separating the tables for a CROSS JOIN.
3.
How do you avoid a Cartesian Product or a CROSS JOIN?
Do not omit a join clause.
4.
What is the only relational operator used for an equijoin?
The equality sign ‘=’.
5.
On a join statement the SELECT clause specifies….
The column names to retrieve.
6.
On a join statement the FROM clause specifies….
The two tables that the database must access.
7.
On a join statement the WHERE clause specifies….
How the tables are joined.
8.
How are rows of data restricted in a join statement using a WHERE clause?
In addition to the join on the FROM statement, other conditions may
apply…looking for a last name, checking if the salary is greater then 2000…
9.
How are column names known to belong to which table in a join?
A table prefix is added to each column name to designate the table it belongs to.
10. List and describe the Oracle Proprietary Joins
Equijoin
Nonequijoin
Outer join
Self join
11. List and describe the SQL Compliant Joins
Cross joins
Natural joins
Using clause
Right Outer joins
Left Outer joins
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Database Programming - Study Guide Sections 3-4
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Full Outer joins
12. How long can table alias be and why use a table alias?
30 characters long, to improve performance due to the computer not having to search
for what column is on what table, should be has short as can be.
13. Once a table alias is used on a FROM, are they always used in the SELECT statement?
Yes
14. To join four (4) tables together, how many join conditions are needed?
Three join conditions.
15. What condition must be present for a nonequijoin?
A nonequijoin is a join condition that does not include an equality sign.
16. When the same column name appears in more than one table, the column name must be
prefixed with ___________________.
The table name.
17. Why use an outer join?
To generate the rows that are missing….if a row does not satisfy a join condition,
the row will not appear.
18. Can the plus sign (outer join) be placed on both sides of a condition clause?
No, only on one side.
19. What is the difference between a LEFT OUTER JOIN, RIGHT OUTER JOIN, and FULL
OUTER JOIN?
Left Outer Join displays the data that satisfies the join condition and the missing
data from the left table that does not satisfy the join condition. Right Outer Join
displays the data that satisfies the join condition and the missing data from the
right table that does not satisfy the join condition. Full Outer Join displays the
data that satisfies the join condition and the missing data from both tables that
does not satisfy the join condition.
20. Why use a self join?
To join a table to itself.
21. What join is based on all columns in the two tables that have the same name?
NATURAL JOIN
22. Can the join above in question #20 be joined with columns with the same name but different
data types, why?
No, the data types must be the same for the data to match.
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23. What join clause will correct the error in question #21?
JOIN USING clause
24. To specify arbitrary conditions or specify columns to join, what join clause is used?
JOIN ON
25. Does every SELECT statement that joins tables have to have a join condition?
Yes, tables must be join before data will be displayed.
26. Create a query to display the employee number, last name, and department name of all
employees who earn a commission.
SELECT e.employee_id, e.last_name, d.department_name
FROM employees e, departments d
WHERE e.department_id = d.department_id
AND e.commission_pct IS NOT NULL;
27. Create a query to display the last name, job, department number, and department name for
all employees who work in Oxford.
SELECT e.last_name, e.job_id, d.department_id, d.department_name
FROM employees e JOIN departments d
ON (e.department_id = d.department_id)
JOIN locations l
ON (d.location_id = l.location_id)
AND l.city = 'Oxford';
28. Create a query to display the last name and employee number along with their manager’s
last name and number. When you are done, modify the statement of display of all
employees including King who has no manager.
SELECT e.employee_id, e.last_name, m.employee_id manager, m.last_name
FROM employees e, employees m
WHERE e.manager_id = m.employee_id;
SELECT e.employee_id, e.last_name, m.employee_id manager, m.last_name
FROM employees e, employees m
WHERE e.manager_id = m.employee_id(+)
29. Create a query to display the employee last name, department name, and location id of all
employees in department 90.
SELECT e.last_name, d.department_name, d.location_id
FROM employees e, departments d
WHERE e.department_id = d.department_id
AND d.department_id = 90;
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