sql server存储过程使用varchar max作为参数

Question

I have a relatively simple website which uses php + mssql. I have various stored procedures that do simple insert and delete work. The problem I am facing is that many of the parameters that I pass into the stored procedure have the same length as the column I will insert the data.

For instance I have a stored procedure to register a user. The stored procedure has a paramater @USERNAME with varchar(12) as the type. the columnn USERNAME in the USER table has the same type with that length. In principle this is not really a problem. But I would rather be able to freely change the USERNAME column length without having to also change the length of the stored procedure parameter.

I can't use table valued parameters since the mssql php drivers doesn't support them.

The only solution I can imagine is to just use varchar(max) for the stored procedure parameters, but is this considered bad practice?

Answer 1

Short answer: Yes.

What would it mean if someone passed in a username that was 2,147,483,647 characters long!? By using varchar(max) you're implying that it would be ok.

I'm in agreement with the comment by @DanGuzman. Table columns should be sized properly in the first place then paramaters and variables should be sized accordingly. If you have to change the size of the table column then you have to propogate that change elsewhere - that's the best practice approach.

Sizing table columns properly isn't always easy though - how long should a username be? 12 seems short to me, 2,147,483,647 definitely too long - somewhere in between? ;) @JohnCappelletti has a valid point too - storage and processing is cheap compared to the cost of change, so err on the large side when sizing.

If varchar(max) is bad, and you don't want to follow best practice, is there a middle ground? Maybe use a factor of 10? Something sufficiently above the actual size but not excessivly so.

The other thing to watch out for, regardless of how you size your parameters, is silent truncation or run-time truncation errors - check lengths explicitly.