为什么 SQL LEN 函数对包含多个字符的字符串返回“1"? [英] Why does SQL LEN function return '1' for a string with several characters?

问题描述

简单的问题 - 为什么当我在下面的查询中打印 @len 变量的值时，我会得到值 1，而不是 12(指定字符串中的字符数)?

Simple question - why when I print the value of the @len variable in the query below would I be getting the value 1, instead of 12 (the number of characters in the specified string)?

DECLARE @string varchar
DECLARE @index int
DECLARE @len int
DECLARE @char char(1)
SET @string = 'content loop'
SET @index = 1
SET @len= LEN(@string)

print @len

推荐答案

您对 @string 的声明是错误的.varchar 没有长度.

Your declaration of @string is wrong. You have no length on the varchar.

试试这个:

declare @string varchar(255);   -- or whatever

您刚刚了解到这种情况下的默认值为 1.

You just learned that the default in this situation is 1.

这在文档中有明确规定.进一步说明，MS SQL 似乎使这变得相当复杂:

This is clearly specified in the documentation. As a further note, MS SQL seems to make this rather complicated:

在数据定义或变量声明中未指定 n 时语句，默认长度为1.当使用时不指定nCAST 和 CONVERT 函数，默认长度为 30.

When n is not specified in a data definition or variable declaration statement, the default length is 1. When n is not specified when using the CAST and CONVERT functions, the default length is 30.

正确的习惯是在使用 varchar 或 nvarchar 时总是包含长度.

The right habit is to always include the length when using varchar or nvarchar.

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