OCR A-Level Computer Science Data exchange and databases overview quiz quiz

It allows the exact original file to be reconstructed

It permanently discards data the eye cannot see

It always achieves a higher compression ratio than lossy

It can only be used on images

A photograph with continuously varying colours

An icon with long runs of identical pixels

Encrypted ciphertext

A list of random numbers

a public key to encrypt and a private key to decrypt

no key at all

the same single key to encrypt and to decrypt

a one-way function that cannot be reversed

Hashing makes the stored password much faster for the user to type in

Hashing compresses the password so that it takes up far less disk space

Hashed passwords can later be decrypted again by the user whenever they are needed

Hashing is one-way, so a stolen database does not directly reveal the passwords

unique for each record with no nulls

identical to the primary key of another related table

always a single numeric field rather than a composite

exactly the same attribute as a foreign key in the table

By storing both of the entities together in one single combined table

With a link (junction) table holding two foreign keys

By simply removing one of the two entities from the design entirely

It cannot be implemented at all in a relational database model

it has a composite key made of several attributes

it still contains some repeating groups of data

no non-key attribute depends on another non-key attribute

every field in the table is allowed to hold multiple values at once

ORDER BY

FROM

INSERT INTO

WHERE

Every record in the table will be updated

The statement will simply refuse to run at all

Only the very first record in the table will change

The whole table will be deleted from the database

returning every single possible combination of the rows from both tables

matching a foreign key in one table to the primary key in the other

permanently deleting all of the unmatched rows from both tables

sorting the rows of both tables into alphabetical order first

the transaction always runs as fast as it possibly can on the server

other concurrent transactions are able to see its partial results

the transaction is all-or-nothing, fully completing or being rolled back

all of the data is fully compressed before it is finally written to storage

Data compression errors that occur when records are written back to the disk

Slow disk access when many records are read at once

Syntax errors in the SQL queries sent to the database

The lost update problem, where simultaneous edits overwrite each other