Introduction to SQL

Retrieving Individual Columns

What is SQL?

Database

Why SQL Matters

SQL is essential for managing and querying databases 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.

Let's get started! In this course, we will work with a country database containing a country table. Let's look at this table.

SQL Syntax Explanation

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, the syntax is:

sql
SELECT sample FROM sample_table;

The following query will return all entries in the continent column from the country table:

SELECT continent FROM country;


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SELECT continent FROM country;

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.

Task

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Write an SQL query to retrieve a capital column from the country table.

_{Once you've completed this task, click the button below the code to check your solution.}

Solution

SELECT capital FROM country;

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Section 1. Chapter 1

SELECT ____ FROM ____;

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Introduction to SQL

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1. Retrieving Data

In this section, we will learn how to use the SQL SELECT statement to get a single table column, multiple table columns, and all table columns. We will also find out how to return unique values.

Retrieving Individual Columns

Retrieving Multiple Columns

Retrieving All Columns

Retrieving Distinct Rows

Limiting Results

Challenge: Find the Population of the Countries

Challenge: Find All Countries

Challenge: Find All Countries With Their IDs

Challenge: Find Country Capitals

Challenge: Find the Regions in Which All Countries Are Located

2. Sorting Retrieved Data

In this section, we’ll explore how to organize and prioritize the data returned by a query using the ORDER BY clause. Placed at the end of a SELECT statement, this clause lets you sort your results by one or multiple columns, either in ascending or descending order, enabling more meaningful and easily interpretable data output.

Challenge: Population Sort

Sorting by Multiple Columns

Challenge: Dual-Sort Query

Specifying Sort Direction

Challenge: Sort the Countries by Region and Capital

Challenge: Sort Capitals in Descending Order

Challenge: Sort Countries in Ascending Order

Challenge: Find Countries, Their IDs, and Their Populations

Challenge: Find Countries, IDs, Populations, Regions, and Sort Them

Challenge: Find All Continents and Sort Them in Ascending Order

3. Filtering Data

In this section, we will learn how to filter returned data using the SELECT statement's WHERE clause. We will learn how to test for equality, inequality, more and less significant than value ranges, and NULL values.

Using the WHERE Clause

Challenge: North America Population Sort

The WHERE Clause Operators

Challenge: Population Threshold Query

Checking for a Range of Values

Checking for NO Value

4. Advanced Data Filtering

In this section, we’ll explore how to refine your search conditions by combining WHERE clauses with the AND and OR operators. We’ll also cover how the NOT operator can be used to exclude certain results.

Using the AND Operator

Challenge: Europe Region Sort

Using the OR operator

Challenge: America Regions Filter

Using the NOT Operator

Challenge: Non-Europe Capitals Sort

5. Aggregate Functions

In this section, we will learn what the SQL aggregate functions are and how to use them to summarize table data.

The AVG() Function

Challenge: Surface Area Selection

The COUNT() Function

Challenge: Continental Count

The MAX() Function

The MIN() Function

Challenge: Large Surface Area Average

The SUM() Function