Character Types v13
The following table lists the general-purpose character types available in Advanced Server:
| Name | Description |
|---|---|
CHAR[(n)] | Fixed-length character string, blank-padded to the size specified by n |
CLOB | Large variable-length up to 1 GB |
LONG | Variable unlimited length. |
NVARCHAR(n) | Variable-length national character string, with limit |
NVARCHAR2(n) | Variable-length national character string, with limit |
STRING | Alias for VARCHAR2 |
VARCHAR(n) | Variable-length character string, with limit (considered deprecated, but supported for compatibility) |
VARCHAR2(n) | Variable-length character string, with limit |
Where n is a positive integer; these types can store strings up to n characters in length. An attempt to assign a value that exceeds the length of n will result in an error, unless the excess characters are all spaces, in which case the string will be truncated to the maximum length.
The storage requirement for data of these types is the actual string plus 1 byte if the string is less than 127 bytes, or 4 bytes if the string is 127 bytes or greater. In the case of CHAR, the padding also requires storage. Long strings are compressed by the system automatically, so the physical requirement on disk may be less. Long values are stored in background tables so they do not interfere with rapid access to the shorter column values.
The database character set determines the character set used to store textual values.
CHAR
If you do not specify a value for n, n will default to 1. If the string to be assigned is shorter than n, values of type CHAR will be space-padded to the specified width (n), and will be stored and displayed that way.
Padding spaces are treated as semantically insignificant. That is, trailing spaces are disregarded when comparing two values of type CHAR, and they will be removed when converting a CHAR value to one of the other string types.
If you explicitly cast an over-length value to a CHAR(n) type, the value will be truncated to n characters without raising an error (as specified by the SQL standard).
VARCHAR, VARCHAR2, NVARCHAR and NVARCHAR2
If the string to be assigned is shorter than n, values of type VARCHAR, VARCHAR2, NVARCHAR and NVARCHAR2 will store the shorter string without padding.
Note: The trailing spaces are semantically significant in VARCHAR values.
If you explicitly cast a value to a VARCHAR type, an over-length value will be truncated to n characters without raising an error (as specified by the SQL standard).
CLOB
You can store a large character string in a CLOB type. CLOB is semantically equivalent to VARCHAR2 except no length limit is specified. Generally, you should use a CLOB type if the maximum string length is not known.
The longest possible character string that can be stored in a CLOB type is about 1 GB.
Note: The CLOB data type is actually a DOMAIN based on the PostgreSQL TEXT data type. For information on a DOMAIN, see the PostgreSQL core documentation at https://www.postgresql.org/docs/current/static/sql-createdomain.html
Thus, usage of the CLOB type is limited by what can be done for TEXT such as a maximum size of approximately 1 GB.
For usage of larger amounts of data, instead of using the CLOB data type, use the PostgreSQL Large Objects feature that relies on the pg_largeobject system catalog. For information on large objects, see the PostgreSQL core documentation at:
https://www.postgresql.org/docs/current/static/largeobjects.html