April 1, 2009 at 8:11 am
That might be an old habit of people who worked with earlier versions of SQL Server. The 255 was the maximum supported by the server.
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April 6, 2009 at 9:07 pm
Jacek0 is right. There is no performance advantage to a given maximum length for varchar columns. In fact, for very short columns the overhead of using varchar might outweigh the "unused" bytes of a char column. Using varchar(x), where x is some integer, essentially amounts to a maximum length constraint. This can be useful but, as stated before, the maximum length doesn't buy you any performance gains.
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April 7, 2009 at 12:05 pm
Hi
The 2^n-1 logic comes from old systems because the last character was a 0-character which terminated the string. New systems usually do not use this termination and are optimized to handle any size of strings.
Greets
Flo
April 7, 2009 at 2:27 pm
Some systems used first byte to hold number of characters of string with a maximum of 255 bytes.
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