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In this video you'll learn how to write your first SQL query: retrieving all information from one table.
Definitions
Syntax The vocabulary and grammatical rules surrounding the structure of your code.
Keywords The vocabulary words of a programming language used to issue commands to a computer.
SQL Used
SELECT * FROM <table name>;
The asterisk or star symbol (*) means all columns.
The semi-colon (;) terminates the statement like a period in sentence or question mark in a question.
Examples:
SELECT * FROM books;
SELECT * FROM products;
SELECT * FROM users;
SELECT * FROM countries;
See all of the SQL used in SQL Basics in the SQL Basics Cheat Sheet.
To recap, SQL or Structured Query Language
0:00
is a specialized language to get
information or data out of a database.
0:04
There are many different
database systems such as MySQL,
0:09
Microsoft SQL Server, Oracle,
PostgreSQL, and SQLite.
0:13
All of them use the same language, SQL.
0:18
Just like spoken languages, programming
languages have their own vocabulary and
0:21
grammatical structure.
0:25
Programmers refer to this vocabulary and
grammar as syntax.
0:27
Thankfully, most programming languages
have a much smaller vocabulary
0:30
than spoken languages.
0:34
Though they are few,
0:36
the vocabulary words in programming
languages are very important.
0:37
And we call them key words.
0:41
[SOUND] A keyword is a command that you
issue to a computer to do a certain thing.
0:42
And SQL has its own sets of keywords.
0:48
Lines of SQL code unknown
as a Statement or a Query.
0:51
A statement in SQL is like
a sentence in English.
0:56
A query in SQL is like asking
a question in English.
0:59
Most queries, no matter how complex,
are issued to the database one at a time.
1:03
You may hear the issuing of a statement
being referred to as running a query, or
1:09
executing the SQL.
1:14
Let's take a look at a common SQL query.
1:16
We will treat all information from
the table with the data about books.
1:19
Remember, a table is one of
the spreadsheet like structures
1:24
inside a database made up of rows and
columns.
1:27
Let's see how we might write
a query in English first.
1:31
[SOUND] What is all the information we
have about each book in the books table?
1:36
Now, let's see the SQL syntax to
bring back all the information from
1:41
the books table.
1:44
See there's upper case words there,
select and from.
1:45
They are key words or special words
reserved for the SQL programming language.
1:48
You issue a select command when
you want to write a query.
1:54
You're asking the database to select or
1:58
retrieve some of the information
from a particular table.
2:00
In this case, it's books.
2:04
The asterisk, or the star character,
means you want to bring
2:06
all of the information in all
of the tables, columns back.
2:09
I'll show you how to bring back
specific columns of information later.
2:13
The semicolon at the end of
the query is like a period or
2:17
a question mark at the end
of a sentence or question.
2:21
The semicolon lets the database know
where the statement ends or terminates.
2:24
When we issue the statement
to the database,
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you can expect all entries in
the books table to be returned.
2:31
Let's see the results of this
query in the SQL playground and
2:35
see this query in action.
2:39
As you can see, it brings back all
information in the books table.
2:42
Let's ask another question.
2:46
Who are all the users of
the library in the patrons table?
2:48
We'd use the SELECT keyword.
2:52
Stop, meaning all of the columns.
2:55
From, and then the table name.
2:58
In this case, the table name is patrons.
3:00
Don't forget the semicolon
to terminate the statement.
3:04
Once we execute this query,
it will return all patron information.
3:07
So generally speaking,
writing SELECT * FROM <table name>
3:12
is a query we can use to
retrieve all data from any table.
3:17
This can be useful for small data sets.
3:22
When you have larger data sets like
the users of a large social network, or
3:25
the orders from a popular e-commerce site,
you probably don't want to run queries
3:30
like this because it can take a very long
time to execute and return the results.
3:35
This can slow the performance down for
other database users too.
3:40
However, the data sets in this
course are very small, and
3:44
running these types of queries were
having a real performance impact.
3:48
Databases have more utility than reporting
all the information in one table.
3:52
In the next video, I'll show you
how to bring back specific columns.
3:57
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