The recommended data type for storing data with less than 128 characters for improved performance is VARCHAR(128). Using VARCHAR(128) allows for efficient storage because it allocates only the space necessary to store the actual string length, as long as it does not exceed 128 characters. This is particularly beneficial in contexts where performance and storage efficiency are critical, as it can reduce overhead associated with fixed-length data types.
Unlike VARCHAR(MAX), which is intended for variable-length strings that could be very large, using a specific length such as VARCHAR(128) ensures that the database engine can optimize memory usage and processing time. Additionally, CHAR(128) would allocate a fixed-size space for 128 characters even if the actual data is shorter, leading to unnecessary waste of storage. On the other hand, NVARCHAR(128) is used for storing Unicode data, which is necessary when supporting multiple languages, but it uses twice the storage for each character compared to VARCHAR. In scenarios where Unicode support isn't needed and character lengths are limited to less than 128, VARCHAR(128) would be the most efficient choice.