What does order by in mysql mean?

The ORDER BY clause sorts MySQL query results by specified criteria. Syntax: SELECT ...ORDER BY column(s) [ASC|DESC] Usage: Add an ORDER BY clause at the end of the SELECT statement. Sort multiple columns: Use multiple columns to sort in the specified order. Sorting NULL value: Default minimum value, can be modified using IS NULL. Performance: Use ORDER BY on indexed columns to improve performance.

ORDER BY

Definition

ORDER BY clause uses Used to sort MySQL query results according to specified criteria.

Syntax

<code>SELECT ...
ORDER BY column(s) [ASC|DESC]</code>

Where:

• column(s): Specifies the column used for sorting. Multiple columns can be specified, arranged in the specified order.
• ASC/DESC: Optional keyword, specify ascending order (ASC) or descending order (DESC) sorting. Default is ASC.

Usage

To sort the query results, add an ORDER BY clause at the end of the SELECT statement. For example:

<code>SELECT *
FROM table_name
ORDER BY name ASC;</code>

This will sort the query results by the name column in ascending order (smallest to largest).

Sort multiple columns

You can use multiple columns to sort query results. For example:

<code>SELECT *
FROM table_name
ORDER BY name ASC, age DESC;</code>

This will sort first by the name column in ascending order, then by the age column in descending order (largest to smallest).

Sort NULL values

By default, NULL values ​​are treated as the smallest value in sorting. To change this behavior, you can use the IS NULL condition:

<code>SELECT *
FROM table_name
ORDER BY name ASC NULLS LAST;</code>

This will cause the NULL value to appear as the largest value in the sort.

Performance Considerations

Using ORDER BY on indexed columns can improve query performance. Without indexes, MySQL would need to scan the entire table to sort, which can take a lot of time and resources.

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