So,
As far as I understand the only varchar advantage is trimming of blank
spaces of data, and disadvantages are disk space.

Ann W. Harrison wrote:

>Adomas Urbanavicius wrote:
>
>
>>Hello,
>>But according to claimed VARCHAR disk saving space,
>>
>>
>
>Varchar will use more space than char on disk - no one disputes that, or
>any one who does should have been corrected. Varchar fields have a two
>byte length at the front, followed by the character string. Char fields
>have just the character string. Both are blank filled (unless they're
>charset octets). Run length compression turns the trailing blanks into
>two bytes per 255 characters.
>
>If you store a single character 'A' in a 200 byte character field, what
>will be written to disk (probably, it depends on the values in
>surrounding fields), is 1 byte of length indicating that the next byte
>is data, one byte with the character 'A', a second byte of length
>(negative in this case) indicating that the next byte is to be repeated
>199 times,
>and the character ' ' <- blank. Total, 4 bytes.
>
>If you store a single character 'A' in a varchar field, what will be
>written to disk (same caveat) is one byte indicating that the next three
>bytes are significant, three bytes containing 0x0, 0x1, and 'A',
>followed by a second length byte containing -199 that indicates that the
>next byte is to be repeated 199 times, then the trailing byte of blank.
> Total 6 bytes. 50% more storage.
>
>
>
>>This shows that varchar uses up to 10% more of disk space.
>>
>>
>
>Your test includes fixed page and record overhead. Other than that,
>it's the second worst case - worst case is an all blank string following
>a string with trailing blanks. In that case, the char field takes no
>space at all, while the varchar takes four bytes.
>
>
>
>>Made selection :
>>select field1 from table1
>> group by field1
>>CHAR DB : ~55sec
>>VARCHAR : ~65sec
>>
>>
>
>Lots of other factors can affect performance, without a lot more detail
>I'd be hesitant to say which type was faster. One area where varchar
>has a performance advantage is remote transmission. There, the trailing
>blanks are passed for char and not for varchar.
>
>My advice is to use char for values that are actually fixed length -
>postal codes, US social security numbers, etc., and varchar for values
>that vary in length. The time you spend trimming off trailing blanks
>totally negates any tiny saving in on disk space.
>
>Regards.
>
>
>Ann
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