VARCHAR(255) stores 255 characters, which may be more than 255 bytes.
Yes, is matter when you indexing multiple columns. Prefixes can be up to 1000 bytes long (767 bytes for InnoDB tables). Note that prefix limits are measured in bytes, whereas the prefix length in CREATE TABLE statements is interpreted as number of characters.
VARCHAR is a variable-length character data type. The default length is 80, and the maximum length is 65000 octets. For string values longer than 65000, use Long Data Types. Values can include trailing spaces.
255 is used because it's the largest number of characters that can be counted with an 8-bit number. It maximizes the use of the 8-bit count, without frivolously requiring another whole byte to count the characters above 255.
In sql server does it make a difference if I define a varchar column to be of length 32 or 128?
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