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Editorial Team
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Asked: 2026-05-15T16:19:33+00:00

I have a database with a field that holds permit numbers associated with requests.

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I have a database with a field that holds permit numbers associated with requests. The permit numbers are 13 digits, but a permit may not be issued.

With that said, I currently have the field defined as a char(13) that allows NULLs. I have been asked to change it to varchar(13) because char’s, if NULL, still use the full length.

Is this advisable? Other than space usage, are there any other advantages or disadvantages to this?

I know in an ideal relational system, the permit numbers would be stored in another related table to avoid the use of NULLs, but it is what it is.

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  1. Editorial Team

    Well, if you don’t have to use as much space, then you can fit more pages in memory. If you can do that, then your system will run faster. This may seem trivial, but I just recently tweaked the data types on a a table at a client that reduced the amount of reads by 25% and the CPU by about 20%.

    As for which is easier to work with, the benefits David Stratton mentioned are noteworthy. I hate having to use trim functions in string building.

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