Joe Celko's SQL for Smarties, 3rd Edition

Chapter 5. Character Data Types in SQL

SQL-89 DEFINED A CHARACTER(n) or CHAR(n) data type, which represents a fixed-length string of (n) printable characters, where (n) is always greater than zero. Some implementations allow the string to contain control characters, but this is not the usual case. The allowable characters are usually drawn from ASCII or EBCDIC character sets and most often use those collation sequences for sorting.

SQL-92 added the VARYING CHARACTER(n) or VARCHAR(n), which was already present in many implementations. A VARCHAR(n) represents a string that varies in length from 1 to (n) printable characters. This is important: SQL does not allow a string column of zero length, but you may find vendors whose products do allow it ...