varchar vs text - MySQL

Question

in my project an user can write comment [plain text], and view others comment, can delete own comment, but can not update comment !
In this case which would should i use ?

Text or Varchar(4048) ?
What is the advantage and disadvantage of Text and Varchar(large like 4000) ?
Is it secure enough if i replace only '<' with '& lt;' and '>' with '& gt;' to make sure everything is fine ?
[i dont want to convert all those like ' " & ..., to save space, i just want to make sure user can not write javascript]

There will be a limit on the front end

Solution 1

To protect yourself from XSS attack, encode it using the htmlentities function.

Other than that, the choice of datatype has most to do with how big the content will be. If it may exceed 4048 characters, then use a text datatype. If many posts will be large, using a text datatype may reduce wasted data space and may perform slightly better than a giant varchar, but it depends upon your situation, you would be best to test the alternatives.

I generally prefer varchar because it's easier to deal with from a coding perspective, if nothing else, and fall back to text if the contents may exceed the size of a varchar.

Solution 2

Varchar is usually faster in retrieval when the size is reasonable, as it is stored within the table, where as TEXT is stored off the table with a pointer to location.

Thanks

Solution 3

(You have multiple questions; I will address the one that is in the title.)

The only difference between VARCHAR(4000) and TEXT is that an INSERT will truncate to either 4000 characters or 65536 bytes, respectively.

For smaller values than 4000, there are cases where the temp table in a complex SELECT will run faster with, for example, VARCHAR(255) than TINYTEXT. For that reason, I feel that one should never use TINYTEXT.

Solution 4

it depends on the application behavior. space allocated inside block's table decrease space for other columns and decrease density data inside it. if full table scan is used by mysql, many blocks are scanned, it's inefficient. so it depends on your sql requests.

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Comments

[Sourav]

will it be faster too if the varchar size is 4000 ? And thnx for replying :)

[Just a PHP Programmer]

It depends on what hardware you are using, you would better do a benchmark for it. Thanks...

[Sourav]

i was just waiting to hear that XSS, how can someone do XSS with out < and >, coz i think without < and > the script lost it's power, it will be appreciated if you can give some example of exactly which character to convert(htmlentitles) to be safe ?

[squawknull]

There is some potential for increased data file fragmentation in many databases if you have a lot of large values stored in varchars. With mysql, it gets even more complex as it depends upon how the specific storage engine works (and this is always subject to change). Hence, if I think most of the fields will be on the smaller end of the scale, just use varchar. If many will be large, use text.

[squawknull]

Don't try to piecemeal the characters. Particularly as you get outside of the UTF8 characterset, things get very tricky. Using the htmlentities function is the simplest, best bet you have, and I can't think of a reason not to just use it versus trying to do something else yourself. There are lots of examples at php.net/manual/en/function.htmlentities.php.

[zac1987]

using TEXT won't increase data file fragmentation?

[Rick James]

The "stored off the table" is referring to certain ROW_FORMATs in InnoDB. Both VARCHAR(4000) and TEXT are subject to such, so this is not really a difference.

[Rick James]

htmlentities should be used when displaying text, not when storing into the database.