Section 11 - Databases

Question 1

What are the 4 main SQL commands

Answer 1

SELECT
UPDATE
DELETE
INSERT

Question 2

sql select syntax

Answer 2

SELECT <attribute>
FROM <table>
WHERE <condition>
ODER BY <attribute> <ASC/DESC></attribute></condition></attribute>

Question 3

sql update syntax

Answer 3

UPDATE <table>
SET <attribute> = <value>
WHERE <attribue> = <value></value></attribue></value></attribute>

Question 4

sql delete syntax

Answer 4

DELETE FROM <table>
WHERE <condition></condition>

Question 5

sql insert syntax

Answer 5

INSERT INTO <table>
VALUES (<value1>, <value2>, ...)</value2></value1>

Question 6

sql create syntax

Answer 6

CREATE TABLE <table>(<attribute> <datatype> PRIMARY KEY, <attribute> <datatype>, ...)</datatype></attribute></datatype></attribute>

Question 7

what is record locks

Answer 7

• when a record is accessed by a user it is locked to other users until they’re finished
• this means others cannot access or modify the content

Question 8

what is serialisation

Answer 8

• requests to access records are put in a queue
• after the first user has finished using the record the next command in the queue is executed

Question 9

what is timestamp ordering

Answer 9

• each command about a feild is assigned a timestamp when it is initiated
• commands are carried out in the order of their timestamps

Question 10

commitment ordering

Answer 10

an algorithm is used to work out an optimum order to execute commands on the same feild