Order by

An   clause in SQL specifies that a SQL  statement returns a result set with the rows being sorted by the values of one or more columns. The sort criteria does not have to be included in the result set (restrictions apply for,  ,  ,   and  .) The sort criteria can be expressions, including column names, user-defined functions, arithmetic operations, or   expressions. The expressions are evaluated and the results are used for the sorting, i.e., the values stored in the column or the results of the function call.

is the only way to sort the rows in the result set. Without this clause, the relational database system may return the rows in any order. If an ordering is required, the  must be provided in the   statement sent by the application. Although some database systems allow the specification of an  clause in subqueries or view definitions, the presence there has no effect on the final result-set order, but makes sense when combined with a result offset clause or a fetch first clause. A view is a logical relational table, and the relational model mandates that a table is a set of rows, implying no sort order whatsoever. The only exception are constructs like  (not standardized in SQL:2003) which allow the propagation of sort criteria through nested subqueries.

The SQL standard's core functionality does not explicitly define a default sort order for Nulls. With the SQL:2003 extension T611, "Elementary OLAP operations", nulls can be sorted before or after all data values by using the  or   clauses of the   list, respectively. Not all DBMS vendors implement this functionality, however. Vendors who do not implement this functionality may specify different treatments for Null sorting in the DBMS.

Structure   will order in descending order, otherwise ascending order is used. (The latter may be specified explicitly using  .)

Examples
This sorts by the LastName column, then by the FirstName column if LastName matches.