How to Use SELECT in SQL? - Example and Implementation

Recipe Objective - How to Use SELECT in SQL? - Example and Implementation  

Structured Query Language (SQL) is the foundation of database management and plays a pivotal role in extracting, manipulating, and managing data. The SELECT statement is arguably the most frequently used SQL command, allowing you to retrieve data from a database. Read this recipe to explore how to use SELECT in SQL, providing detailed examples and practical implementations to help you harness the power of SQL for data retrieval and analysis.

How to Use SELECT Query in SQL? 

The SELECT statement is one of the most frequently used SQL queries. It is used to retrieve data from one or more tables. The data is displayed in a table which is known as the result set.

Basic Syntax:

SELECT column_name1, column_name2,...

FROM table_name;

SELECT  * in SQL 

The Syntax to select all the data from a table is as follows:

SELECT  * 

FROM table_name;

Let us select all the fields from the customers table that has columns employee_id, employee_name, age, city, and country. 

Code:

SELECT * FROM customers;

Output:

 +-------------+----------------+------+------------+---------+

| employee_id | employee_name  | age  | city       | country |

+-------------+----------------+------+------------+---------+

|         101 | Thomas Shelby  |   30 | Birmingham | England |

|         102 | Grace Burgess  |   28 | Dublin     | Ireland |

|         103 | Alfie Solomons |   40 | London     | England |

|         104 | Michael Gray   |   22 | New York   | USA     |

|         105 | May Carleton   |   29 | Sheffield  | England |

+-------------+----------------+------+------------+---------+

5 rows in set (0.00 sec)

If we just want to view the customer_id and customer_name columns from the table, we can do so using the following query –

Code:

SELECT employee_id, employee_name FROM customers;

Output:

+-------------+----------------+

| employee_id | employee_name  |

+-------------+----------------+

|         101 | Thomas Shelby  |

|         102 | Grace Burgess  |

|         103 | Alfie Solomons |

|         104 | Michael Gray   |

|         105 | May Carleton   |

+-------------+----------------+

5 rows in set (0.00 sec)

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DISTINCT Keyword in SQL 

The distinct keyword is used alongside the SELECT statement to retrieve distinct i.e. unique values of data.

Syntax:

SELECT DISTINCT column_name1, column_name2, ... 

FROM table_name;

Now, let us retrieve the distinct values from the income column of the customers table.

Code:

SELECT DISTINCT income 

FROM customers;

Output:

+----------+

| income   |

+----------+

| 90000000 |

| 10000000 |

| 78000000 |

| 56000000 |

+----------+

4 rows in set (0.01 sec)

We can see that the value 78000000 that appeared twice in the actual table, has been displayed only once when the DISTINCT keyword is used.

GCP Data Ingestion with SQL using Google Cloud Dataflow

TOP Keyword in SQL 

The TOP keyword is used alongside the SELECT statement to retrieve the top n number or n percent of rows. It is similar to what head function does in other programming languages.

Syntax:

SELECT TOP number/percent column_name1, column_name2, ... 

FROM table_name;

Example 1: Let us retrieve the top 3 incomes from the customers table. 

Code:

SELECT TOP 3 income FROM customers;

Example 2: Let us retrieve 40 Percent of income data from customers tables.

Code:
SELECT TOP 40 PERCENT income from customers;

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