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Editorial Team
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Asked: 2026-05-12T09:17:55+00:00

I am starting a new project, and I am considering using alias data types

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I am starting a new project, and I am considering using alias data types in my SQL Server 2005 database, for common table columns. For e.g. I would define an alias data type to hold the name of an object, as follows:

CREATE TYPE adt_Name FROM
varchar(100) not null

Then use it for the definition of table columns, ensuring all my columns share the exact same definition (length, nullability, precision, etc).

  1. What are the advantages of using alias data types?
  2. What are the disadvantages of using alias data types?
  3. What naming conventions would you recommend? I was thinking adt_Xxx (adt = alias data type).
  4. Why does SQL Server 2005 Management Studio not allow me to work with alias data types from the GUI. I can only use them through SQL Scripts. The GUI doesn’t list them in any of the drop-down boxes – its frustrating.
  5. How will the use of alias data types affect my Linq to SQL model?
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1 Answer

  1. Editorial Team

    Advantages:

    • Reusable and Sharable, the ADT is reusable within the database it’s created in, if you want it across all your DBs then create it in the model database

    • Enforcement, the ADT will enforce the characteristics, length and nullability of it’s base type, and can be used to enforce development standards

    • Disallows implicit conversions, ADTs cannot be CAST or CONVERTed

    • Simplicity, as with other languages, ADTs lend simplicity to development and maintenance

    • Data Hiding

    Disadvantages:

    • Unmodifiable, ADTs cannot be directly modified, you must DROP and reCREATE them. Note that you can still ALTER the tables they’re in to another base type or ADT, then DROP and reCREATE them, then ALTER the tables back (or just CREATE a new one to alter them to).

    • No Tools, ADTs must be created with a direct query using the CREATE statement (sp_addtype is deprecated and shouldn’t be used).

    • Table variables are not supported

    Naming Conventions:

    • ‘adt_’ looks like it will work just fine

    Linq to SQL:

    • Treat these types as either the base type in your querys, or create the corresponding type to use
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