Column Length declaration

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Column Length declaration

Arsh

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Points: 6354
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November 8, 2017 at 8:03 am

#326155

Dear Experts,
On starting to design for a new project , I would like to know if its better to allocate double the size of the data-length anticipated to grow or to declare a length little more than what is anticipated to grow maximum. Or is it just better to give a much longer length without bothering about anything ? are there any implications of giving too long column lengths with varchar ? Int and Char are understandable though. Thank you in advance.

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John Mitchell-245523 SSC Guru Points: 148809 More actions · Answer 1

No, just make it the length it needs to be and no more, otherwise you'll get inaccurate memory grants and other such nasties when you start to run queries.

John

Bill Talada SSChampion Points: 11954 More actions · Answer 2

Error slightly on the short side. It is safer to loosen rather than tighten constraints in the future - and length is a constraint. Screen and report layout widths are based on defined column lengths. Large column widths will leave a developer bewildered about screen and report designs. Some internal limitations are based on actual and others on declared sizes like little land mines that may eventually blow up.

Thom A SSC Guru Points: 99130 More actions · Answer 3

Like John said, assign it to the size it should be. Databases grow, Tables, grow, but columns should not. You should know how large a field is going to be when you create your database/application. For example, you a reference might be between 8 and 12 characters, so make it a varchar(12); don't make it a varchar(24) incase, one day, just maybe, you *might* have a 13 character reference.

If you're using an IDENTITY column, then choose an appropriate size still. If you know a table isn't going to have more than 10,000 records inserted into in, then you could use a smallint. If you want to really cover yourself create the column as a smallint IDENTITY(-32768,1); you'll have over 64,000 values to play with then.

Queue Joe telling me off for defining a numeric column that I have no plan to do maths on.

Thom~

Excuse my typos and sometimes awful grammar. My fingers work faster than my brain does.
Larnu.uk

Arsh SSCertifiable Points: 6354 More actions · Answer 4

Thanks John , Thom A and Bill .
Thom, your approach seems suitable especially for systems with not-so-high memory if we look from the memory-grant perspective. Since SQL estimates the column data-occupied length to be half, and does the memory grant , what's the magnitude of impact when it knows that the actual grants required are little more because , a varchar(12) has occupancy above 6 (8 to 12) in your example ? I mean is it a costly operation that may impact performance ?