The ORDER BY clause of a SELECT statement specifies which columns are to be used for ordering the rows in the result table. The ORDER BY clause is sometimes referred to as the "sort by" clause.

The sorting order of each column in the ORDER BY clause specifies whether the column is to be in ascending or descending order in the result table.

The sequence of the columns in the ORDER BY clause specifies the sequence the rows will be sorted by in the result table. This means that the result table will first be sorted by the first column in the ORDER BY clause, then within that ordering the result table will be sorted by the second column in the ORDER BY clause, and so on.

The ORDER BY clause is optional. If it is not specified, the result table will not be sorted.