This MariaDB tutorial explores all of the comparison operators used to test for equality and inequality, as well as the more advanced operators.
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Description
Comparison operators are used in the WHERE clause to determine which records to select. Here is a list of the comparison operators that you can use in MariaDB:
| Comparison Operator | Description |
|---|---|
| = | Equal |
| <=> | Equal (Safe to compare NULL values) |
| <> | Not Equal |
| != | Not Equal |
| > | Greater Than |
| >= | Greater Than or Equal |
| < | Less Than |
| <= | Less Than or Equal |
| IN ( ) | Matches a value in a list |
| NOT | Negates a condition |
| BETWEEN | Within a range (inclusive) |
| IS NULL | NULL value |
| IS NOT NULL | Non-NULL value |
| LIKE | Pattern matching with % and _ |
| EXISTS | Condition is met if subquery returns at least one row |
Let's review the comparison operators that you can use in MariaDB.
Example - Equality Operator
In MariaDB, you can use the = operator to test for equality in a query. The = operator can only test equality with values that are not NULL.
For example:
In this example, the SELECT statement above would return all rows from the sites table where the site_name is equal to 'TechOnTheNet.com'.
Example - Equality Operator (Safe with NULL Values)
Because the = operator only compares non-NULL values, it is not safe to use with NULL values. To overcome this limitation, MariaDB added the <=> operator to allow you to test for equality with both NULL and non-NULL values.
To better explain the difference between the = operator and the <=> operator, we will include some examples with both queries and data.
Assuming that we have a table called sites in MariaDB that is populated with the following data:
| site_id | site_name | server1 | server2 |
|---|---|---|---|
| 1 | TechOnTheNet.com | MyServer | <NULL> |
| 2 | CheckYourMath.com | <NULL> | <NULL> |
| 3 | DigMinecraft.com | TBD | TDB |
| 4 | BigActivities.com | MyServer | Other |
We could use the = operator in the following query:
Because we used the = operator, we would get the following results:
| contact_id | last_name | website1 | website2 |
|---|---|---|---|
| 3 | DigMinecraft.com | TBD | TDB |
In this example, the SELECT statement above would return all rows from the sites table where server1 is equal to server2. It does not return the second record where server1 and server2 are both NULL values.
Now let's see what happens when we rewrite our query using the <=> operator that is safe to use with NULL values:
Because we used the <=> operator, we would get the following results:
| contact_id | last_name | website1 | website2 |
|---|---|---|---|
| 2 | CheckYourMath.com | <NULL> | <NULL> |
| 3 | DigMinecraft.com | TBD | TDB |
Now our query returns all rows from the sites table where server1 is equal to server2, including those records where server1 and server2 are NULL values.
Example - Inequality Operator
In MariaDB, you can use the <> or != operators to test for inequality in a query.
For example, we could test for inequality using the <> operator, as follows:
In this example, the SELECT statement would return all rows from the sites table where the site_name is not equal to 'DigMinecraft.com'.
Or you could also write this query using the != operator, as follows:
Both of these queries would return the same results.
Example - Greater Than Operator
You can use the > operator in MariaDB to test for an expression greater than.
In this example, the SELECT statement would return all rows from the sites table where the site_id is greater than 3. A site_id equal to 3 would not be included in the result set.
Example - Greater Than or Equal Operator
In MariaDB, you can use the >= operator to test for an expression greater than or equal to.
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In this example, the SELECT statement would return all rows from the sites table where the site_id is greater than or equal to 3. In this case, site_id equal to 3 would be included in the result set.
Example - Less Than Operator
You can use the < operator in MariaDB to test for an expression less than.
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In this example, the SELECT statement would return all rows from the sites table where the site_id is less than 50. A site_id equal to 50 would not be included in the result set.
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Example - Less Than or Equal Operator
In MariaDB, you can use the <= operator to test for an expression less than or equal to.
In this example, the SELECT statement would return all rows from the sites table where the site_id is less than or equal to 50. In this case, site_id equal to 50 would be included in the result set.
Example - Advanced Operators
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We've written specific tutorials to discuss each of the more advanced comparison operators in MariaDB. These topics will be covered later, or you can jump to one of these tutorials now.