How sorting is done in SQL using ORDER BY, DESC and ASC

Sorting Results

We looked at how to get data from our tables using the SELECT command. Results were returned in the same order the records were added into the database. This is the default sort order. In this section, we will be looking at how we can sort our query results.Sorting is simply re-arranging our query results in a specified way. Sorting can be performed on a single column or on more than one column. It can be done on number, strings as well as date data types.

 

Order by clause

The order by clause is used to sort the query result sets in either ascending or descending order. It is used in conjunction with the SELECT query. It has the following basic syntax.

 

SELECT statement... [WHERE condition | GROUP BY `field_name(s)` HAVING condition] ORDER BY `field_name(s)` [ASC | DESC];

HERE

  • "SELECT statement..." is the regular select query
  • " | " represents alternatives
  • "[WHERE condition | GROUP BY `field_name(s)` HAVING condition" is the optional condition used to filter the query result sets.
  • "ORDER BY" performs the query result set sorting
  • "[ASC | DESC]" is the keyword used to sort result sets in either ascending or descending order. Note ASC is used as the default.

What are DESC and ASC Keywords?

altASC is the short form for ascending

altDESC is the short form for descending

It is used to sort the query results in a top to bottom style.

It is used to sort the query results in a bottom to top style

When working on date data types, the earliest date is shown on top of the list.

. When working on date types, the latest date is shown on top of the list.

When working with numeric data types, the lowest values are shown on top of the list.

When working with numeric data types, the highest values are shown at top of the query result set.

When working with string data types, the query result set is sorted from those starting with the When working with string data types, the query result set is sorted from those starting with the letter Z going down to the letter A letter A going up to the letter Z.

When working with string data types, the query result set is sorted from those starting with the letter Z going down to the letter A.

 

Both the DESC and ASC keywords are used together in conjunction with the SELECT statement and the ORDER BY clause.

DESC and ASC syntax

The DESC sort keyword has the following basic syntax.

SELECT {fieldName(s) | *} FROM tableName(s) [WHERE condition] ORDER BY fieldname(s) ASC /DESC [LIMIT N]

HERE

  • SELECT {fieldName(s) | *} FROM tableName(s) is the statement containing the fields and table(s) from which to get the result set from.
  • [WHERE condition] is optional but can be used to filter the data according to the given condition.
  • ORDER BY fieldname(s) is mandatory and is the field on which the sorting is to be performed. The DESC keyword specifies that the sorting is to be in descending order.
  • [LIMIT] is optional but can be used to limit the number of results returned from the query result set.

Examples:

Let's now look at a practical example -

SELECT * FROM members;
 

Executing the above script in MySQL workbench against the myflixdb gives us the following results shown below.

alt

Let's suppose the marketing department wants the members details arranged in decreasing order of Date of Birth.  This will help them send birthday greetings in a timely fashion. We can get the said list by executing a query like below -

SELECT * FROM members ORDER BY date_of_birth DESC;

Executing the above script in MySQL workbench against the myflixdb gives us the following results shown below.

alt

The same query in ascending order

SELECT * FROM members ORDER BY date_of_birth ASC

alt

Note: NULL values means no values (not zero or empty string) . Observe the way they have been sorted.

More examples

Let's consider the following script that lists all the member records.

SELECT * FROM `members`;

Executing the above script gives the following results shown below.

alt

Suppose we want to get a list that sorts the query result set using the gender field, we would use the script shown below.

SELECT * FROM `members` ORDER BY `gender`;

alt

"Female" members have been displayed first followed by "Male" members, this is because when order by clause is used without specifying the ASC or DESC keyword, by default, MySQL has sorted the query result set in an ascending order.

Let's now look at an example that does the sorting using two columns; the first one is sorted in ascending order by default while the second column is sorted in descending order.

SELECT * FROM `members` ORDER BY `gender`,`date_of_birth` DESC;

Executing the above script in MySQL workbench against the myflixdb gives the following results.

alt

The gender column was sorted in ascending order by default while the date of birth column was sorted in descending order explicitly

Why we may use DESC and ASC?

Suppose we want to print a payments history for a video library member to help answer queries from the front desk, wouldn't it be more logical to have the payments printed in a descending chronological order starting with the recent payment to the earlier payment? The DESC key word comes in handy in such situations. We can write a query that sorts the list in descending order using the payment date. Suppose the marketing department wants to get a list of movies by category that members can use to decide which movies are available in the library when renting movies, wouldn't it be more logical to look sort the movie category names and title in ascending so that members can quickly lookup the information from the list? The ASC keyword comes in handy in such situations; we can get the movies list sorted by category name and movie title in an ascending order.

Summary

  • Sorting query results is re-arranging the rows returned from a query result set either in ascending or descending order.
  • The DESC keyword is used to sort the query result set in a descending order.
  • The ASC keyword is used to sort the query result set in an ascending order.
  • Both DESC and ASC work in conjunction with the ORDER BY keyword. They can also be used in combination with other keywords such as WHERE clause and LIMIT
  • The default for ORDER BY when nothing has been explicitly specified is ASC.

 

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