Question

I want to know how SQL Server handles varchar dynamic length and storage internally.

Is there beneficial to use Varchar if i know that i have fixed length of character is coming in column ?

I know difference between CHAR and VARCHAR, but what’s best way to use in big database for database design CHAR or VARCHAR ?

Answer 1

CHAR allocates its size in row, VARCHAR stores real size of string (2 bytes) and then the real string, so overhead of varchar is +2 bytes, and overhead of CHAR is – its size minus real string length. If in varchar stored NULL value – its size in db is Zero.

See Anatomy of the Record

record header
    4 bytes long
    two bytes of record metadata (record type)
    two bytes pointing forward in the record to the NULL bitmap
fixed length portion of the record, containing the columns storing data types that have fixed lengths (e.g. bigint, char(10), datetime)
NULL bitmap
    two bytes for count of columns in the record
    variable number of bytes to store one bit per column in the record, regardless of whether the column is nullable or not (this is

different and simpler than SQL Server 2000 which had one bit per
nullable column only)
this allows an optimization when reading columns that are NULL
variable-length column offset array
two bytes for the count of variable-length columns
two bytes per variable length column, giving the offset to the end of the column value
versioning tag
this is in SQL Server 2005 only and is a 14-byte structure that contains a timestamp plus a pointer into the version store in
tempdb