A string is a sequence of characters up to 2 GB in size. A string can occur in SQL:
as a string literal. A string literal is a sequence of characters enclosed in single quotes (apostrophes). A string literal represents a particular, constant value, and it may contain escape sequences for special characters that cannot be easily typed as characters. See Binary literals.
as the value of a column or variable with a CHAR or NCHAR data type.
as the result of evaluating an expression.
The length of a string can be measured in two ways:
Byte length The byte length is the number of bytes in the string.
Character length The character length is the number of characters in the string, and is based on the character set being used.
For single-byte character sets, such as cp1252, the byte-length and character-length are the same. For multibyte character sets, a string's byte-length is greater than or equal to its character-length.