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Sorting

The default sort order, for the data returned by a SQL query, is ascending. In this sort order:

·         numeric values are displayed with the lowest values first; for example, 1 to 999

·         date values are displayed with the earliest value first; for example, 01-JAN-92 before 01-JAN-95

·         character values are displayed in the alphabetical order; for example, "A" first and "Z" last

·         null values are displayed last for ascending sequences and first for descending sequences

·         you can also sort by a column that is not in the SELECT list

Here are some examples that depict sorting:

1. To reverse the order in which the rows are displayed, specify the DESC keyword after the column name in the ORDER BY clause. This sample code sorts the result by the most recently hired employee.
   
   SELECT last_name, job_id, department_id, hire_date
   FROM employees
   ORDER BY hire_date DESC ;
2.  You can also use a column alias in the ORDER BY clause. This sample code sorts the data by annual salary.
   
   SELECT employee_id, last_name, salary*12 annual
   FROM employees
   ORDER BY annual ;
3. You can sort query results by specifying the numeric position of the column in the SELECT clause. This sample code sorts the result by department_id, as this column is at the third position in the SELECT clause.
   
   SELECT last_name, job_id, department_id, hire_date
   FROM employees
   ORDER BY 3;
4. You can sort query results by more than one column. The sort limit is the number of columns in the given table. In the ORDER BY clause, you specify the columns and separate the column names using commas. If you want to reverse the order of a column, specify DESC after its name, as in this sample code.
   
   SELECT last_name, department_id, salary
   FROM employees
   ORDER BY department_id, salary DESC;

Order of Precedence

The rules of precedence determine the order in which expressions are evaluated and calculated. You can override the default order by using parenthesis around the expressions that you want to calculate first. This table lists the default Order of Precedence

1. Arithmetic Operators
2. Concatenation Operator
3. Comparison Conditions
4. IS [NOT] NULL, LIKE, [NOT] IN
5. [NOT] BETWEEN
6. Not Equal to
7. NOT logical condition 
8. AND 
9. OR