Introduction to SQL | Exam prep questions

Introduction to SQL


Terms in this set (64)


is a programming language for user interaction with
What is SQL definition
databases, used to query, update, and manage
databases.
A database is an organized structure designed to store,
What is SQL database definition
modify, and process large amounts of data.
SQL is essential for managing and querying databases
Why SQL Matters efficiently. It is widely used due to its standardization,
scalability, and ability to ensure data integrity. SQL's
integration with other technologies makes it a versatile tool
in various applications, supporting real-time data
processing and decision-making.
To retrieve data from a database, SQL uses the SELECT
statement. Here's the basic syntax:


SELECT: Specifies the columns to retrieve;
FROM: Specifies the table from which to retrieve the data.
For example, to get the sample column from the sample_table table,
SQL Syntax Explanation the syntax is:

SELECT sample FROM sample_table;
In our previous query, we utilized the SELECT to retrieve a
single continent column from the country table. It's
important to note that you must specify the column name
immediately after the SELECT keyword, and the FROM
keyword specifies the name of the table from which we
wish to retrieve data.

, This table contains 15 rows,
representing 15 unique records for
various countries.


The table includes 7 columns: id,
name, continent, region,
SurfaceArea, capital, and
Table
population.
id - the unique identifier for
each record; name - the
name of the country;
continent - the continent where the
country is located;
region - the specific region within the
continent; SurfaceArea - the total
land area of the country; capital -
the capital city of the country;
population - the number of people
living in the country.


To retrieve multiple columns, use the SELECT statement. After
SELECT, list the column names you want to retrieve,
separated by commas.
The Syntax for
The syntax looks like this:
Selecting Multiple 1 SELECT column1, column2, column3
Columns 2 FROM table_name;

Here's an example of how to select three columns from the country
table:
1 SELECT id, name, capital
2 FROM country;
Write an SQL query to retrieve the continent and population
The Syntax for columns from the country table.
Selecting Multiple
Columns-2 Select continent, population from country
Instead of listing each column, you can use the asterisk * to
retrieve all columns from the table at once. This is
Retrieving All Columns
especially useful when you need to view all the data in a
table without manually typing out each column name.


Example: select* from country;
Note that the SELECT statement returns all rows in a given
column. However, what if we don't need all the values
Retrieving Distinct Rows from a column, especially when they are duplicated,
and we only need unique values?

, For such cases, it is convenient to use the keyword
DISTINCT, placed immediately before the column names.
Let's take a look at an example:
We know that the SELECT operator can retrieve all rows
from a table of all or the specific columns. However, what
if we only need to fetch a specific number of rows?


We can do it using the LIMIT clause. It is always used at the
end of the query. Here is the syntax for it:

Limiting Results
1. SELECT columns
2. FROM table
3. LIMIT number_of_rows;



In the example below, we extract the first 7 rows (in our case,
the capitals of the countries) from the column:


select distinct continent from country limit 7;
Challenge: Find the Population select population from country
of the Countries