AQA A-Level Computer Science databases and SQL overview quiz quiz

An entity is simply one of the many individual properties that together happen to make up a single attribute

An entity is a real-world thing the database stores data about; an attribute is a property of it

They are two interchangeable words that mean exactly the same thing in database design

An attribute is the structure that links two entities together across separate tables

By deleting one of the two entities so that only a single one-to-many link remains

By merging the two separate tables into one single wide table holding all the attributes

By adding a linking (junction) table, creating two one-to-many relationships

It cannot be resolved in a relational database and must be avoided altogether

To uniquely identify each record within its own table, in the way a primary key does

To sort the records in the table into a defined order

To encrypt the sensitive data values stored in the table

To link two tables by referring to another table's primary key

Update, insertion and deletion anomalies

Noticeably faster queries across the whole database

A consistently smaller overall file size on disk

Stronger built-in encryption of the stored data

It contains repeating groups of data within a single row, holding several different values inside one and the same field

It is in 2NF and has no transitive dependencies, so every non-key attribute depends only on the primary key

It is built from at least three separate tables that are joined together by relationships

It deliberately uses no foreign keys at all to link to any of the other tables

SELECT

FROM

WHERE

ORDER BY

SELECT Name WHERE Mark > 60 FROM Student ORDER BY Mark ASCENDING;

FROM Student SELECT Name WHERE Mark > 60 SORT BY Mark DESC;

SELECT Name FROM Student ORDER BY Mark > 60 WHERE DESC;

SELECT Name FROM Student WHERE Mark > 60 ORDER BY Mark DESC;

Without it, every record in the table is deleted

It is needed to sort the deleted records into the correct order

Including the WHERE clause makes the DELETE query run noticeably faster

WHERE is simply not allowed inside a DELETE statement at all

Several separate transactions are all able to run in parallel at the same time

A transaction completes fully or has no effect at all

Once committed, the changes made by a transaction are permanent and survive failures

The database always stays in a valid and consistent state after every change

By permanently deleting any records that are currently held under a lock by a transaction

By automatically encrypting every record at the moment a lock is placed on it

When two transactions each hold a record the other needs and each waits for the other

Record locking on its own can never cause a deadlock under any circumstances

Atomicity

Consistency

Durability

Isolation