- 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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Your First SQL Statement
4:01In this video, you'll learn how to write your first SQL query: retrieving all information from one table.
To recap, SQL or Structured Query Language
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is a specialized language to get
information or data out of a database.
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There are many different
database systems such as MySQL,
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Microsoft SQL Server, Oracle,
PostgreSQL, and SQLite.
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All of them use the same language, SQL.
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Just like spoken languages, programming
languages have their own vocabulary and
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grammatical structure.
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Programmers refer to this vocabulary and
grammar as syntax.
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Thankfully, most programming languages
have a much smaller vocabulary
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than spoken languages.
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Though they are few,
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the vocabulary words in programming
languages are very important.
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And we call them key words.
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[SOUND] A keyword is a command that you
issue to a computer to do a certain thing.
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And SQL has its own sets of keywords.
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Lines of SQL code are known
as a Statement or a Query.
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A statement in SQL is like
a sentence in English.
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A query in SQL is like asking
a question in English.
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Most queries, no matter how complex,
are issued to the database one at a time.
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You may hear the issuing of a statement
being referred to as running a query, or
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executing the SQL.
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Let's take a look at a common SQL query.
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We'll retrieve all information from
the table with the data about books.
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Remember, a table is one of
the spreadsheet like structures
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inside a database made up of rows and
columns.
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Let's see how we might write
a query in English first.
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[SOUND] What is all the information we
have about each book in the books table?
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Now, let's see the SQL syntax to
bring back all the information from
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the books table.
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See those upper case words there,
SELECT and FROM?
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They are key words or special words
reserved for the SQL programming language.
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You issue a select command when
you want to write a query.
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You're asking the database to select or
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retrieve some of the information
from a particular table.
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In this case, it's books.
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The asterisk, or the star character,
means you want to bring
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all of the information in all
of the tables' columns back.
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I'll show you how to bring back
specific columns of information later.
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The semicolon at the end of
the query is like a period or
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a question mark at the end
of a sentence or question.
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The semicolon lets the database know
where the statement ends or terminates.
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When we issue the statement
to the database,
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you can expect all entries in
the books table to be returned.
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Let's see the results of this
query in the SQL playground and
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see this query in action.
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As you can see, it brings back all
information in the books table.
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Let's ask another question.
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Who are all the users of
the library in the patrons table?
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We'd use the SELECT keyword,
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star, meaning all of the columns,
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FROM, and then the table name.
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In this case, the table name is patrons.
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Don't forget the semicolon
to terminate the statement.
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Once we execute this query,
it will return all patron information.
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So generally speaking,
writing SELECT * FROM <table name>;
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is a query we can use to
retrieve all data from any table.
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This can be useful for small data sets.
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When you have larger data sets like
the users of a large social network, or
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the orders from a popular e-commerce site,
you probably don't want to run queries
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like this because it can take a very long
time to execute and return the results.
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This can slow the performance down for
other database users too.
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However, the data sets in this
course are very small, and
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running these types of queries won't
have any real performance impact.
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Databases have more utility than reporting
all the information in one table.
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In the next video, I'll show you
how to bring back specific columns.
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