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You don't need to just search for equal or unequal values. You can compare them to a value you decide.
Relational Operators
There are several relational operators you can use:
-
<less than -
<=less than or equal to -
>greater than -
>=greater than or equal to
These are primarily used to compare numeric and date/time types.
SQL Used
SELECT <columns> FROM <table> WHERE <column name> < <value>;
SELECT <columns> FROM <table> WHERE <column name> <= <value>;
SELECT <columns> FROM <table> WHERE <column name> > <value>;
SELECT <columns> FROM <table> WHERE <column name> >= <value>;
Examples:
SELECT first_name, last_name FROM users WHERE date_of_birth < '1998-12-01';
SELECT title AS "Book Title", author AS Author FROM books WHERE year_released <= 2015;
SELECT name, description FROM products WHERE price > 9.99;
SELECT title FROM movies WHERE release_year >= 2000;
See all of the SQL used in SQL Basics in the SQL Basics Cheat Sheet.
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SQL isn't only used for finding or
filtering on exact matches,
0:00
it can be used to compare values
using relational operators.
0:05
The name of relational
operators comes from their
0:09
usage in comparing the relationship
between two values,
0:12
not because they're used
in a relational database.
0:16
These operators are actually found in
many of the programming languages,
0:19
not just SQL.
0:23
So let's take a look at
the operators we already know.
0:24
The equality or equal to operator
compares the quality of two values.
0:28
The text of Andrew is the same
as the text of Andrew.
0:33
So this condition is true.
0:37
The inequality operator, or
the not equal to operator,
0:39
compares the values, and if they
don't match, the condition is true.
0:43
The text of Andrew is not the same as
the text of Lauren, so this is true.
0:48
Now onto the relational operators.
0:54
You tend to see these operators
when comparing numbers and dates.
0:56
We're going to focus on numbers first.
1:00
The first one we're going to look
at is the less than operator,
1:02
which is represented by
a left angle bracket.
1:06
All operators read from left to right.
1:09
If the value on the left-hand side of
the operator is smaller than the value on
1:12
the right side of the operator,
the condition will evaluate to true.
1:16
If the two values are equal to each other,
the condition will evaluate to false,
1:21
because the left value is not
smaller than the right value.
1:26
In this example, all values less than 40,
but not including 40, are true.
1:30
If you wanted to compare values
less than or equal to each other,
1:36
you'd use the less than operator,
followed by the equals sign.
1:40
This is known as the less than or
equal to operator.
1:44
This is just like the less than operator,
but
1:48
it is inclusive of the value
on the right hand side.
1:50
How about creating values
greater than a particular value?
1:54
Well, we use the right angle bracket or
the greater than symbol.
1:58
100 is greater than 40 and 99,
but is not greater than 100.
2:02
However, 100 is greater than or
equal to 100.
2:09
Let's use these new operators to answer
some more questions from our database.
2:13
Let's start with the question
what books are in the library
2:18
that were first published after 2005?
2:22
Let's start with our
general SQL statement.
2:26
SELECT * FROM books.
2:28
Then let's add a where clause,
2:34
first_published is greater than 2005.
2:38
Notice how Harry Potter and
the Half Blood Prince wasn't selected,
2:45
since it's first published
year was in 2005.
2:52
2005 isn't greater than itself,
it is equal to itself.
2:55
If we wanted to include books from 2005
too, we should use the greater than or
3:01
equal to operator to get all
books from 2005 onwards.
3:06
Finally, let's find some
classics in our library.
3:11
Let's find all books released
before the 20th century.
3:14
How would you change this query?
3:18
That's right.
3:21
We would change the greater than or
equal to operator to be the less than
3:23
operator and the value 1900.
3:29
Nice.
3:35
Obviously, 1900 is the beginning
of the 20th Century.
3:37
But if we wanted to include 1900, we'd
use the less than or equal to operator.
3:40
Our results are the same since we have
no books in our library from 1900.
3:47
With these comparison
operators under your belt,
3:50
you can now filter your
data in more exciting ways.
3:54
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