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    <p><em>So why do people try to make their columns as small as possible?</em> I don't believe in making them as small as possible, but sizing them appropriately. Some reasons for making (n)varchars smaller rather than larger:</p> <p>1) With a larger field, all clients that use the database must be able to handle the full size. For example, take a system that holds a United States address with 255 characters per each field: (Similar to TDWTF that you reference, I believe.)</p> <ul> <li>First Name </li> <li>Last Name</li> <li>Address Line 1</li> <li>Address Line 2</li> <li>City</li> <li>State </li> <li>ZIP Code</li> </ul> <p>Now your data entry screens will need to allow and show 255 characters per field. Not hard, but unlikely to look nice with larger fields Printing invoices, you will need line breaking logic to handle the large fields. Depending on tool, not that hard. </p> <p>But I would not want the problem of formatting the address for an envelope that could have 255 characters for each of those fields or just any one of those fields. Are you going to truncate if the field is too long to fit? Great someone has Address Line 1 of "House Number Streat Number ... blah blah blah ... Appartment number 111." And you'll lop off the important apartment number. Are you going to wrap? How much? What if you just can't fit it in the little box of space on the envelop? Raise an exception and have someone hand letter it?</p> <p>2) While 10 characters of data held in a varchar(50) versus varchar(255) does not impact size or speed, allowing 255 characters allows for more space to be taken. And if all fields are that large you could hit size limits in SQL Server 2000. (I haven't read up on 2005 &amp; 2008 to see if they can handle rows greater than one page.) And with Oracle you the larger sizes allows row chaining to happen if someone actually uses all the available characters.</p> <p>3) Indexes have stricter size limits then leaf pages. You may preclude indexes, especially composite indexes, if you create your varchars too big.</p> <hr> <p>On the other hand, I have a long line 1 for my address, and have been frustrated by web sites that don't allow the full thing to be typed.</p>
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    1. CO1) If there really is a size limit (like the available space on an envelope), then it does make sense to put a limit there, that I already noted in my question. But I would rather prefer to make the limit in my client app than in the DB. Because if the limit ever changed, I would then only have to change the client app - in most cases a task far easier than doing a DB schema update.
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    2. CO2) Row size is a point, however since most real data will not reach these limits, it is quite unlikely that a row so big will be met. The large sizes are meant more for fail-safe than actual use.
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    3. CO3) Another point - but my thoughts are the same as in 2).
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