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Why is the default length for VARCHAR 30 when using CAST?

Answer 1

+5 A:

Why don't you specify the varchar length? ie:

select cast('the quick brown fox jumped over the lazy dog' as varchar(45))

As far as why 30, thats the default length in SQL server for that type

Edit: Moved this up from my comment:

wanted to double check the default length statement...here it specifies it on MSDN http://msdn.microsoft.com/en-us/library/ms176089.aspx first sentence under "Remarks"

curtisk 2008-12-11 13:13:14

+1. Why wouldn't you set the length? Not setting it is asking for trouble.

Bert Evans 2008-12-11 17:19:13

It was a quick and dirty query, so that why I didn't specify. Thanks for pointing me to the docs though where it is mentioned though.

edosoft 2008-12-12 10:49:57

Answer 2

+2 A:

I don't know why they chose 30, but it was the same in Sybase SQL Server, which Microsoft's SQL Server was developed from. It seems to be a peculiarity of those RDBMSs as it's not in the SQL standards, and other servers differ in their behaviour.

xahtep 2008-12-11 13:13:25

According to the SQL standard, a cast to VARCHAR with no length should be a cast to VARCHAR(1). That's not useful - so you should always provide a length. There's a case that 30 is a better default than 1; I'd even agree. But why 30 instead of 25, 32, 40, 64, ... aaah; that way lies madness!

Jonathan Leffler 2008-12-11 13:43:50

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Why is the default length for VARCHAR 30 when using CAST?

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