When querying data, if no sorting operation is used, by default SQL will arrange the query results in the order in which tuples are added.
To perform sorting operations in SQL, you can use the keyword ORDER BY.... After this keyword, you can add the keyword ASC (ascend) to indicate ascending order (from small to large), and DESC (descend) to indicate descending order (from large to small).
If ASC or DESC is not added after the ORDER BY... keyword to indicate ascending or descending order, SQL will default to ascending ASC order. As shown in the following code:
SELECT employee_id, last_name, salary FROM employees ORDER BY salary;
Query results:
##[Example 1] Query employee tableemployees The employee's
employee_id,
last_name,
salary and
department_id information. And sort by
salary from largest to smallest (descending order).
SELECT employee_id, last_name, salary FROM employees ORDER BY salary DESC;Query results: 2. Use column aliases to sort In SQL, you can use fields (columns) Alias to sort. Because sometimes we need to calculate fields that are not in the table (such as annual salary
annual_salary), or some field names are really too long, using short aliases can improve the efficiency of our programming. As shown in the following example:
employee_id,
last_name, and monthly salary
salary# of the employees in the employee table employees
## and annual salaryannual_salary
information. And sorted by annual_salary
from largest to smallest (descending order). <pre class="brush:sql;">SELECT employee_id, last_name, salary,
salary * (1 + IFNULL(commission_pct, 0) * 12) AS "annual_salary"
FROM employees
ORDER BY annual_salary DESC;</pre>
Query results:
[Note]
Must be declared after FROM
.
, not in WHERE
. **If you use column aliases in WHERE
, SQL will report an error. So why can’t column aliases in MySQL be used in WHERE
? The reasons are as follows:
SELECT employee_id, last_name, department_id FROM employees WHERE department_id IN(50, 60, 70) ORDER BY department_id DESC;
3. Second-level sorting
[Example 1] Query the employee ID
employee_id, name last_name
, of the employees in the employee table employees
, Monthly salary salary
and department ID department_id
. And first sort by department ID department_id
in descending order, and then sort by salary
from large to small (descending order). <pre class="brush:sql;">SELECT employee_id, last_name, salary, department_id
FROM employees
ORDER BY department_id DESC, salary DESC;</pre>
Query results:
## and so on. You can add a comma after ORDER BY
to achieve level three and level four&hellip ; Sort.The above is the detailed content of How to sort data in MySQL. For more information, please follow other related articles on the PHP Chinese website!