add Clustered Index option in DDL statement.

[coocood]

Feature Request

Is your feature request related to a problem? Please describe:

The clustered index feature is table specific.
Use a session variable to control it is not intuitive and error prone.
If only some of the tables should use the clustered index feature, the user has to change the variable in the code back and forth.

Describe the feature you'd like:

Make clustered index a table option instead of a session variable.
The variable is still kept with global scope only, so users can use the clustered index without the need to change the code.

Describe alternatives you've considered:

Teachability, Documentation, Adoption, Migration Strategy: