We can use another form of variable expansion to select a specific substring, based on a specific character offset and length. Try typing in the following lines under bash.
可以根据特定字符偏移和长度，使用另一种形式的变量扩展，来选择特定子字符串。
Remember that UTF-8 encodes data an a variable-length format; the Unicode character at position 450 simply needed two bytes to be encoded in UTF-8.
记住UTF-8编码的数据是可变长的格式；450处的Unicode字符在使用 UTF-8 进行编码时实际上只需要两个字节。
The description column is a variable-length character string, so it expects a string (which you indicate by enclosing the character data within single quotes).
description列是长度可变的字符串，所以它预计是一个字符串(通过将字符数据括在单引号中指明)。
Variable-length character string having maximum length size bytes or characters.
具有最大长度的带有字符集属性的可变长度的字符类型。
Variable-length character string having maximum length size bytes or characters.
具有最大长度的带有字符集属性的可变长度的字符类型。
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