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24 Cards in this Set

  • Front
  • Back

Define SQL

SQL: (Structured Query Language): is a standard language for accessing and manipulating information in a relational database.

The language consists of SQL commands and is an ANSI (American National Standards Institute) Standard, but there are slightly different flavours (versions)

Name the common flavours





-MSQL (Microsoft)

-Microsoft Access

Most implementations do not implement the entire standards but they all implement the basics

Basic form of an SQL Query

SELECT column_name

FROM table_name

WHERE condition_is_true

Define each of the commands in the basic query structure

SELECT: Get the data you want, normally column names, sometimes a function of a column.

FROM: Find the table

WHERE: find the rows which satisfy this condition, can be dropped

How to access data from a relational database

Use SQL queries which are made up of commands such as SELECT, FROM, WHERE, etc.

These can then potentially return a result from the database

SQL Case sensitivity, state for commands and data

-SQL commands are not case sensitive, however conventionally all capitals

-Data is case sensitive

Convention for writing queries

-SQL commands: all capitals (SELECT)

-Table names: start with capital (Student)

-Column names: all lower-case (fname)

What must SQL queries start with, and what must they include and what can they potentially include

All SQL queries start with a keyword (SELECT) this tells the DBMS what type of operation is going to be executed.

They must include the table which to operate on

They can potentially include columns which are affected by the operation


Sometimes results are repeated, so we use SELECT DISTINCT if we only want distinct column values.

This command must always be followed with a col_name

Define all operators for the WHERE clause

>: Greater than

<: Less than

<>: Not equal

>=: Greater than or Equal to

<=: Less than or Equal to

BETWEEN: Between an inclusive range

IN: In a specified set of values

NOT NULL: The column has a value

IS NULL: The column has no value

Give examples using IN for string and integers and the logical operator it uses


WHERE position IN 'Manager' OR 'Supervisor'

Considers case of both manager and supervisor


WHERE studentID IN (1,3,7)

Considers case of studentID with 1,3 or 7

IN is based on the OR operator

Give examples of using BETWEEN for strings and integers and state the range and logical operator

BETWEEN range is inclusive and is based on the AND operator


WHERE salary BETWEEN 5000 AND 10000


WHERE recipes BETWEEN 'apples' AND 'pears'

What do NOT IN and NOT BETWEEN do

They consider the entries outside of the ranges stated

What does IS NULL do and write a command with it

IS NULL considers columns which have no value, note this is different than an empty string or 0.

WHERE address IS NULL;

How must we always close of a query

With ;

What does IS NOT NULL do

This considers columns which are not null, note it would also return empty strings or 0

Define an AND quality

Means two conditions must be true

Define an OR qualtiy

Either of the two conditions must be true


Use this command to order the results which are returned by the query



ASC: ascending order (default)

DSC: descending order

Note; this command must always be the last in the query

Define aggregate functions

Return a single value, calculated from values in a column

General syntak of a function query and useful aggregate functions

SELECT FUNCTION_NAME(col_name) FROM Table_name






State what these three queries return


SELECT COUNT (salary) FROM Employee


1) Returns the number of rows in the table

2) Returns the number of rows in which salary is not null

3) Returns the number of different salaries in the table

Describe what GROUP BY does, with an examples

Returns values from aggregate functions for distinct groups

SELECT COUNT(staffID), school FROM Lecturer GROUP BY school

Returns the number of lecturers in each school

If listing columns in a query, how must they be seperated

With commas