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SQL Basics

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Retrieving Specific Columns of Information

2:53 with Andrew Chalkley

You don't have to retrieve all the information from a table. You can retrieve only the information you want from the columns you want and filter out the rest.

SQL Used

Retrieving a single column:

SELECT <column name> FROM <table name>;

Examples:

SELECT email FROM users;
SELECT first_name FROM users;
SELECT name FROM products;
SELECT zip_code FROM addresses;

Retrieving multiple columns:

SELECT <column name 1>, <column name 2>, ... FROM <table name>;

Examples:

SELECT first_name, last_name FROM customers;
SELECT name, description, price FROM products;
SELECT title, author, isbn, year_released FROM books;
SELECT name, species, legs FROM pets;

See all of the SQL used in SQL Basics in the SQL Basics Cheat Sheet.

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    In the previous video we used the select star from table query to retrieve all 0:00
    information in a table, but you may not want to bring back all the information. 0:05
    Often you want a smaller subset of information. 0:10
    This can be particularly helpful if you don't want to bring back sensitive 0:13
    information. 0:17
    Like the addresses or dates of birth. 0:18
    Let's take a look at some simple ways to retrieve only some 0:21
    of the information in a table. 0:24
    Let's start with all the information from the patrons table. 0:26
    And we can filter it down from there. 0:30
    The asterisk, or star, is short hand for all of the column names in the table. 0:34
    Now, what if I wanted to retrieve only the emails from our patrons table? 0:39
    We still want to select something from our patrons table. 0:44
    So our query mostly stays the same. 0:48
    All we need to do is change the asterisk, remember? 0:50
    An asterisk is shorthand for everything. 0:54
    We can replace it with the column name we want. 0:57
    In this case, it's email. 1:00
    As you can see this selects all the emails from our patrons table. 1:05
    Let's try one more. 1:10
    What if we wanted all the first names in our patrons table. 1:12
    You can probably guess what we need to do. 1:15
    You just to write the name of the first name column, first_name, 1:17
    between the select and from keywords. 1:22
    Okay, let's change that back. 1:27
    Having either all columns or a single column returned back has limited utility. 1:33
    Remember, the power of SQL is that you can retrieve any subset of information 1:38
    from a table without being destructive to the underlying data. 1:43
    Nothing is deleted, it's just presented differently. 1:47
    Let's say I wanted to send out a library newsletter talking about the new books 1:52
    available to loan. 1:56
    How do I go about retrieving both the first name and 1:58
    email address of each patron? 2:00
    In other words, 2:02
    how do I select two columns of data from the database with one query? 2:03
    SQL makes this kind of task pretty easy on us. 2:08
    I can simply separate the name for 2:11
    each column I want with a comma in the SQL query. 2:13
    The great thing is that I can change the ordering of the columns how I see fit. 2:19
    Since the recap, the area between the SELECT and 2:34
    the FROM keywords is the columns you want to get the information from. 2:37
    SELECT * FROM patrons is a lot shorter than including all of the column names. 2:42
    You're a better person than me if you can remember all the column names. 2:46
    Let's do some code challenges to solidify what we've learned here. 2:49

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