order by Clause Restrictions

Restrictions for using the order by clause.

The maximum number of columns allowed in an order by clause is 400.
You cannot use order by on text, unitext, or image datatype columns.
Subqueries and view definitions cannot include an order by clause (or a compute clause or the keyword into). Conversely, you cannot use a subquery in an order by list.
You cannot update the result set of a server- or language- type cursor if it contains an order by clause in its select statement. For more information about the restrictions applied to updatable cursors, see the Transact-SQL User’s Guide.
If you use compute by, you must also use an order by clause. The expressions listed after compute by must be identical to or a subset of those listed after order by, must be in the same left-to-right order, must start with the same expression, and must not skip any expressions. For example, if the order by clause is:
```
order by a, b, c
```
the compute by clause can be any (or all) of these:
```
compute by a, b, c 
compute by a, b 
compute by a
```
You can also use the keyword compute can be used without by to generate grand totals, grand counts, and so on. In this case, order by is optional.