This has been puzzling me. At first I thought it was something that Navicat was doing but I also tried in EMS MySQL and it does the same.
If I set the type of a field to varchar and set the length to anything less than 4 it will get converted to a char type of the same length. Now I know that char is faster. I read it can be up to 50% faster but I am curious why I am prevented from having a varchar of length less than 4?
Is it prohibitively expensive to do this in MySQL? Is it such a bad idea that they simply don't allow you to do it? Inquiring minds want to know.
Taking a wild guess here so I might be wrong. Varchar needs a length to be appended to the start of the character data so MySQL can tell how long it is. This length field is probably 2 bytes long. Thus if the max length of the string is 1-3 bytes long, the field will be from 3-5 bytes so you might as well bite-the-bullet and just declare the field as char(4). If the length field is 4 bytes, then ALL Varchars under max=3 will be 5-8 bytes for max=1-3 so again char(4) is shorter.
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