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We're doing a lot of large, but straightforward forms for a fairly big project (about 600 users using it throughout the day - that's big for me at least ;-) ).
The forms have a lot of question/answer type sections, so it's natural for some people to type a sentence, while others type a novel. How beneficial would it be to put a character limit on some of these fields really?
(Please include references or citations, if necessary/possible - Thanks!)
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In most circumstances, VARCHAR provides better performance, it's more flexible, and can be fully indexed. If you need to store longer strings, use MEDIUMTEXT or LONGTEXT, but be aware that very large amounts of data can be stored in columns of these types.
The key difference between varchar and nvarchar is the way they are stored, varchar is stored as regular 8-bit data(1 byte per character) and nvarchar stores data at 2 bytes per character. Due to this reason, nvarchar can hold upto 4000 characters and it takes double the space as SQL varchar.
Please, note that: nvarchar data type is variable-length unicode string data, but max indicates that the maximum storage size is 2^31-1 bytes (2 GB).
Each character of an nvarchar column requires 2 bytes of storage whereas a varchar column requires 1 byte per character. Potentially, varchar will be quicker but that may well mean that you cannot store the data that you need.
If you have no limitations on the data size, then why worry. This doesn't sound like a mission critical project, even with 600 users and several thousand records. Use CLOB/BLOB and be done with it. I have doubts as to whether you would see any major gains in limiting sizes and risking data loss. That said, you should layout such boundaries before implementation.
Usually varchar is best for storing values that you wish to use logically and perform "whole value" comparisons against. Text is for unstructured data. If your project is a survey result with unstructured text, use CLOB/BLOB
Semi-Reference: I work with hundreds of thousands of call center records sometimes where we use a CLOB to store the dialog between employees and customers.
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