- Tools We'll be Using 3:57
- Your First SQL Statement 4:01
- Selecting All Information From a Table 5 objectives
- Retrieving Specific Columns of Information 2:53
- Retrieving Specific Columns of Information 5 objectives
- Categorizing Your Output with 'AS' 4:33
- Categorizing Your Output with 'AS' 4 objectives
- Review & Practice with SQL Playgrounds 1:50
- Getting Data From a Database Review 8 questions
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Retrieving Specific Columns of Information
2:53You 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.
In the previous video we used the select
star from table query to retrieve all
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information in a table, but you may not
want to bring back all the information.
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Often you want a smaller
subset of information.
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This can be particularly helpful if
you don't want to bring back sensitive
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information.
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Like the addresses or dates of birth.
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Let's take a look at some simple
ways to retrieve only some
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of the information in a table.
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Let's start with all the information
from the patrons table.
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And we can filter it down from there.
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The asterisk, or star, is short hand for
all of the column names in the table.
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Now, what if I wanted to retrieve only
the emails from our patrons table?
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We still want to select something
from our patrons table.
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So our query mostly stays the same.
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All we need to do is change the asterisk,
remember?
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An asterisk is shorthand for everything.
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We can replace it with
the column name we want.
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In this case, it's email.
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As you can see this selects all
the emails from our patrons table.
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Let's try one more.
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What if we wanted all the first
names in our patrons table.
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You can probably guess what we need to do.
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You just to write the name of the first
name column, first_name,
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between the select and from keywords.
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Okay, let's change that back.
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Having either all columns or a single
column returned back has limited utility.
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Remember, the power of SQL is that you
can retrieve any subset of information
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from a table without being
destructive to the underlying data.
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Nothing is deleted,
it's just presented differently.
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Let's say I wanted to send out a library
newsletter talking about the new books
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available to loan.
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How do I go about retrieving
both the first name and
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email address of each patron?
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In other words,
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how do I select two columns of data
from the database with one query?
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SQL makes this kind of
task pretty easy on us.
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I can simply separate the name for
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each column I want with
a comma in the SQL query.
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The great thing is that I can change
the ordering of the columns how I see fit.
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Since the recap,
the area between the SELECT and
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the FROM keywords is the columns you
want to get the information from.
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SELECT * FROM patrons is a lot shorter
than including all of the column names.
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You're a better person than me if you
can remember all the column names.
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Let's do some code challenges to
solidify what we've learned here.
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