(SQL Tutorials for Citizen Data Scientist)
SQL SELECT Statement
In this tutorial you will learn how to select records from database tables using SQL.
Selecting Data from Table
In the previous chapter we’ve learned how to insert data in a database table. Now it’s time to select the data from existing tables using the SQL query.
The SELECT
statement is used to select or retrieve the data from one or more tables. You can use this statement to retrieve all the rows from a table in one go, as well as to retrieve only those rows that satisfy a certain condition or a combination of conditions.
Syntax
The basic syntax for selecting the data from a table can be given with:
column1_name
, column2_name
, columnN_name
FROM table_name
;Here, column1_name, column2_name, … are the names of the columns or fields of a database table whose values you want to fetch. However, if you want to fetch the values of all the columns available in a table, you can just use the following syntax:
table_name
;Let’s put these statements into real use. Suppose we’ve a table named employees in our database that contains the following records:
+--------+--------------+------------+--------+---------+ | emp_id | emp_name | hire_date | salary | dept_id | +--------+--------------+------------+--------+---------+ | 1 | Ethan Hunt | 2001-05-01 | 5000 | 4 | | 2 | Tony Montana | 2002-07-15 | 6500 | 1 | | 3 | Sarah Connor | 2005-10-18 | 8000 | 5 | | 4 | Rick Deckard | 2007-01-03 | 7200 | 3 | | 5 | Martin Blank | 2008-06-24 | 5600 | NULL | +--------+--------------+------------+--------+---------+
Select All from Table
The following statement will return all the rows from the employees table.
Example
SELECT * FROM employees;
After execution, the output will look something like this:
+--------+--------------+------------+--------+---------+ | emp_id | emp_name | hire_date | salary | dept_id | +--------+--------------+------------+--------+---------+ | 1 | Ethan Hunt | 2001-05-01 | 5000 | 4 | | 2 | Tony Montana | 2002-07-15 | 6500 | 1 | | 3 | Sarah Connor | 2005-10-18 | 8000 | 5 | | 4 | Rick Deckard | 2007-01-03 | 7200 | 3 | | 5 | Martin Blank | 2008-06-24 | 5600 | NULL | +--------+--------------+------------+--------+---------+
As you can see, it returns all the rows and columns from the employees table.
Tip: The asterisk (*
) is a wildcard character that means everything. For example, the asterisk character in the SELECT
statement of the example above is a shorthand substitute for all the columns of the employees table.
Select Columns from Table
If you don’t require all the data, you can select specific columns, like this:
Example
SELECT emp_id, emp_name, hire_date, salary
FROM employees;
After executing the above statement, you’ll get the output something like this:
+--------+--------------+------------+--------+ | emp_id | emp_name | hire_date | salary | +--------+--------------+------------+--------+ | 1 | Ethan Hunt | 1995-10-30 | 5000 | | 2 | Tony Montana | 1990-07-15 | 6500 | | 3 | Sarah Connor | 2011-04-13 | 5600 | | 4 | Rick Deckard | 2005-10-18 | 7200 | | 5 | Martin Blank | 1996-05-24 | 8000 | +--------+--------------+------------+--------+
As you can see this time there is no dept_id column in the result set. In the next chapter we’ll learn how to select the records from a table based on a condition.
Beginners Guide to SQL – SQL SELECT Statement
Disclaimer: The information and code presented within this recipe/tutorial is only for educational and coaching purposes for beginners and developers. Anyone can practice and apply the recipe/tutorial presented here, but the reader is taking full responsibility for his/her actions. The author (content curator) of this recipe (code / program) has made every effort to ensure the accuracy of the information was correct at time of publication. The author (content curator) does not assume and hereby disclaims any liability to any party for any loss, damage, or disruption caused by errors or omissions, whether such errors or omissions result from accident, negligence, or any other cause. The information presented here could also be found in public knowledge domains.
Learn by Coding: v-Tutorials on Applied Machine Learning and Data Science for Beginners
Latest end-to-end Learn by Coding Projects (Jupyter Notebooks) in Python and R:
All Notebooks in One Bundle: Data Science Recipes and Examples in Python & R.
End-to-End Python Machine Learning Recipes & Examples.
End-to-End R Machine Learning Recipes & Examples.
Applied Statistics with R for Beginners and Business Professionals
Data Science and Machine Learning Projects in Python: Tabular Data Analytics
Data Science and Machine Learning Projects in R: Tabular Data Analytics
Python Machine Learning & Data Science Recipes: Learn by Coding
R Machine Learning & Data Science Recipes: Learn by Coding
Comparing Different Machine Learning Algorithms in Python for Classification (FREE)
There are 2000+ End-to-End Python & R Notebooks are available to build Professional Portfolio as a Data Scientist and/or Machine Learning Specialist. All Notebooks are only $29.95. We would like to request you to have a look at the website for FREE the end-to-end notebooks, and then decide whether you would like to purchase or not.