What is the difference between char and varchar data types in SQL?

CHAR and VARCHAR are data types for storing character strings in SQL relational databases.

The main difference lies in how space is stored and used:

• CHAR(n):

  • Stores fixed-length strings of length n.
  • If the string is shorter than n, the remaining space is filled with spaces.
  • Always uses exactly n bytes of memory, regardless of the actual string length.
  • Processing (reading, writing) can be slightly faster due to fixed length.
  • Suitable for data where the length is always known and constant (e.g., ISO 3166-1 alpha-2 country codes).

• VARCHAR(n):

  • Stores variable-length strings, with a maximum length of n.
  • Uses only the necessary number of bytes to store the string, plus a small additional byte or two to store the actual string length.
  • Can save significant space compared to CHAR if string lengths vary greatly or are often shorter than the maximum.
  • Suitable for variable-length data (e.g., names, addresses, descriptions).

Example table for comparison:

Characteristic	CHAR(10)	VARCHAR(10)
Length type	Fixed	Variable
Memory usage	10 bytes (plus possible metadata)	Actual string length + 1-2 bytes
Storing "hello"	"hello " (padded with spaces)	"hello" (actual length 5 stored)
Storing "helloworld"	"helloworld"	"helloworld"
Padding with spaces	Yes, often trimmed on reading	No
Performance	Slightly faster for read/write	Might be slightly slower due to variable length
Best suited for	Fixed and known length data	Variable length data