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Exam : PostgreSQL CE pgces-02
Title : PostgreSQL CE 8 Silver


1. Table "t1" is defined below.
Table "t1" has a column "id" of type INTEGER, and a column "name" of type TEXT.
t1:
The following SQL is executed while client "A" is connected.
BEGIN;
SELECT * FROM t1 WHERE id = 2 FOR UPDATE;
SELECT * FROM t1 WHERE id = 1 FOR UPDATE; -- (*)
While the second 'SELECT' statement, shown with (*), is being executed, a separate client "B" connects and executes the following SQL.
Select the correct statement about the execution results.
UPDATE t1 SET name = 'turtle' WHERE id = 2;
Note: the default transaction isolation level is set to "read committed".
A. The update process for client "B" is blocked until the current connection for client "A" is finished.
B. The update process for client "B" is blocked until the current transaction for client "A" is finished.
C. The 'UPDATE' process for client "B" proceeds regardless of the condition of client "A".
D. The process of client "B" immediately generates an error.
E. The processes for both clients are blocked, and an error stating that a deadlock has been detected is generated.
Answer: B

2. SQL statements were executed in the following order:
CREATE TABLE fmaster
(id INTEGER PRIMARY KEY, name TEXT);
CREATE TABLE ftrans
(id INTEGER REFERENCES fmaster (id), stat INTEGER, date DATE);
INSERT INTO fmaster VALUES (1, 'itemA');
INSERT INTO ftrans VALUES (1, 1, CURRENT_DATE);
Select two SQL statements that will generate an error when executed next.
A. INSERT INTO ftrans VALUES (1, 1, CURRENT_DATE);
B. INSERT INTO ftrans VALUES (2, 1, '2007-07-07');
C. UPDATE fmaster SET name = 'itemAX' WHERE id = 1;
D. UPDATE fmaster SET id = 100 WHERE id = 1;
E. UPDATE ftrans SET id = 200 WHERE id = 1;
Answer: AC

3. Select two correct descriptions about views.
A. A view is created by 'DECLARE VIEW', and deleted by 'DROP VIEW'.
B. A view is a virtual table which does not exist.
C. A view is created to simplify complicated queries.
D. You can create a view with the same name as already existing tables.
E. A view only exists while the postmaster is running, and is deleted when the postmaster stops.
Answer: BC

4. The "sample" table consists of the following data:
How many rows are returned by executing the following SQL statement?
SELECT DISTINCT ON (data) * FROM sample;
A. 2 rows
B. 3 rows
C. 4 rows
D. 5 rows
E. 6 rows
Answer: B

5. Select two incorrect statements regarding 'DOMAIN'.
A. When defining a domain, you can add a default value and constraints to the original data.
B. Domain is a namespace existing between databases and objects such as tables.
C. A domain is created by 'CREATE DOMAIN'.
D. A domain can be used as a column type when defining a table.
E. To define a domain, both input and output functions are required.
Answer: BE

6. Select two suitable statements regarding the data types of PostgreSQL.
A. One field can handle up to 1GB of data.
B. 'n' in CHARACTER(n) represents the number of bytes.
C. Only the INTEGER type can be declared as an array.
D. There is a non-standard PostgreSQL data type, called Geometric data type, which handles 2-dimensional data.
E. A large object data type can be used to store data of unlimited size.
Answer: AD

7. Select two transaction isolation levels supported in PostgreSQL.
A. DIRTY READ
B. READ COMMITTED
C. REPEATABLE READ
D. PHANTOM READ
E. SERIALIZABLE
Answer: BE

8. PostgreSQL can use an index to access a table. Select two incorrect statements about indexes.
A. An index is created by 'CREATE INDEX', and deleted by 'DROP INDEX'.
B. By using an index effectively, searching and sorting performs faster.
C. There are B-tree, Hash, R-tree and GiST index types.
D. By creating an index, performance always improves.
E. Creating an unused index does not affect the performance of a database at all.
Answer: DE

9. Select two suitable statements regarding the following SQL statement:
CREATE TRIGGER trigger_1 AFTER UPDATE ON sales FOR EACH ROW
EXECUTE PROCEDURE write_log();
A. It is defining a trigger "trigger_1".
B. Every time 'UPDATE' is executed on the "sales" table, the "write_log" function is called once.
C. The "write_log" function is called before 'UPDATE' takes place.
D. 'UPDATE' is not executed if "write_log" returns NULL.
E. 'DROP TRIGGER trigger_1 ON sales;' deletes the defined trigger.
Answer: AE

10. The table "score" is defined as follows:
gid | score
-----+-------
1 | 70
1 | 60
2 | 100
3 | 80
3 | 50
The following query was executed. Select the number of rows in the result.
SELECT gid, max(score) FROM score
GROUP BY gid HAVING max(score) > 60;
A. 1 row
B. 2 rows
C. 3 rows
D. 4 rows
E. 5 rows
Answer: C

11. Select the correct SQL statement which concatenates strings 'ABC' and 'abc' to form 'ABCabc'.
A. SELECT 'ABC' . 'abc';
B. SELECT cat('ABC', 'abc') FROM pg_operator;
C. SELECT 'ABC' + 'abc';
D. SELECT 'ABC' + 'abc' FROM pg_operator;
E. SELECT 'ABC' || 'abc';
Answer: E

12. Select two suitable statements about sequences.
A. A sequence always returns a 4-byte INTEGER type value, so the maximum value is 2147483647.
B. A sequence is defined by 'CREATE SEQUENCE', and deleted by 'DROP SEQUENCE'.
C. Although the "nextval" function is called during a transaction, it will have no effect if that transaction is rolled back.
D. A sequence always generates 0 or consecutive positive numbers.
E. A sequence number can be set by calling the "setval" function.
Answer: BE

13. Table "t1" is defined as follows:
CREATE TABLE t1 (value VARCHAR(5));
A set of SQL statements were executed in the following order. Select the number of rows that table "t1" has after execution.
BEGIN;
INSERT INTO t1 VALUES ('AA');
SAVEPOINT point1;
INSERT INTO t1 VALUES ('BB');
SAVEPOINT point2;
INSERT INTO t1 VALUES ('CC');
ROLLBACK TO point1;
INSERT INTO t1 VALUES ('DD');
END;
A. 1 row
B. 2 rows
C. 3 rows
D. 4 rows
E. 0 rows
Answer: B

14. The following SQL statements were executed using psql.
Select the appropriate statement about the result.
LISTEN sign_v;
BEGIN;
NOTIFY sign_v;
COMMIT;
LISTEN sign_v;
A. At the point that 'NOTIFY sign_v' is executed, a message that starts with "Asynchronous notification 'sign_v' received" is output.
B. At the point that 'COMMIT' is executed, a message that starts with "Asynchronous notification 'sign_v' received" is output.
C. At the point that 'SELECT * FROM pg_user;" is executed, a message that starts with "Asynchronous notification 'sign_v' received" is output.
D. When 'LISTEN sign_v' is executed for the second time, a message that starts with "Asynchronous notification 'sign_v' received" is output.
E. The message "Asynchronous notification 'sign_v' received" is not received while in this connection.
Answer: B