Character types v15

Overview

SQL defines two primary character types: CHARACTER VARYING(n) and CHARACTER(n), where n is a positive integer. These types can store strings up to n characters in length. If you don't specify a value for n, n defaults to 1. Assigning a value that exceeds the length of n results in an error unless the excess characters are all spaces. In this case, the string is truncated to the maximum length. If the string to be stored is shorter than n, values of type CHARACTER are space padded to the specified width (n) and are stored and displayed that way. Values of type CHARACTER VARYING store the shorter string.

If you explicitly cast a value to CHARACTER VARYING(n) or CHARACTER(n), an over-length value is truncated to n characters without raising an error.

The notations VARCHAR(n) and CHAR(n) are aliases for CHARACTER VARYING(n) and CHARACTER(n), respectively. If specified, the length must be greater than zero and can't exceed 10485760. CHARACTER without a length specifier is equivalent to CHARACTER(1). If CHARACTER VARYING is used without a length specifier, the type accepts strings of any size. The latter is a PostgreSQL extension.

In addition, PostgreSQL provides the TEXT type, which stores strings of any length. Although the type T$XT isn't in the SQL standard, several other SQL database management systems have it as well.

Values of type CHARACTER are physically padded with spaces to the specified width n, and are stored and displayed that way. However, trailing spaces are treated as semantically insignificant and disregarded when comparing two values of type CHARACTER. In collations where whitespace is significant, this behavior can produce unexpected results. For example, SELECT 'a '::CHAR(2) collate "C" < E'a\n'::CHAR(2) returns true, even though the C locale considers a space to be greater than a newline. Trailing spaces are removed when converting a CHARACTER value to one of the other string types. Trailing spaces are semantically significant in CHARACTER VARYING and TEXT values and when using pattern matching, that is, LIKE and regular expressions.

The characters that can be stored in any of these data types are determined by the database character set, which is selected when the database is created. Regardless of the specific character set, the character with code zero (sometimes called NUL) can't be stored. For more information, see Character Set Support.

The storage requirement for a short string (up to 126 bytes) is 1 byte plus the actual string, which includes the space padding in the case of CHARACTER. Longer strings have 4 bytes of overhead instead of 1. Long strings are compressed by the system, so the physical requirement on disk might be less. Very long values are also stored in background tables so that they don't interfere with rapid access to shorter column values. In any case, the longest possible character string that can be stored is about 1GB. (The maximum value that's allowed for n in the data type declaration is less than that. It isn't useful to change this value because with multibyte character encodings, the number of characters and bytes can be quite different. If you want to store long strings with no specific upper limit, use TEXT or CHARACTER VARYING without a length specifier, rather than making up an arbitrary length limit.)

Example: Using the character types

CREATE TABLE test1 (a character(4));
INSERT INTO test1 VALUES ('ok');
SELECT a, char_length(a) FROM test1; -- (1)

  a   | char_length
------+-------------
 ok   |           2


CREATE TABLE test2 (b varchar(5));
INSERT INTO test2 VALUES ('ok');
INSERT INTO test2 VALUES ('good      ');
INSERT INTO test2 VALUES ('too long');
ERROR:  value too long for type character varying(5)
INSERT INTO test2 VALUES ('too long'::varchar(5)); -- explicit truncation
SELECT b, char_length(b) FROM test2;

   b   | char_length
-------+-------------
 ok    |           2
 good  |           5
 too l |           5

PostgreSQL has two other fixed-length character types, shown in the following table. These aren't intended for general-purpose use, only for use in the internal system catalogs. The NAME type is used to store identifiers. Its length is currently defined as 64 bytes (63 usable characters plus terminator) but must be referenced using the constant NAMEDATALEN in C source code. The length is set at compile time and is therefore adjustable for special uses. (The default maximum length might change in a future release.) The type "CHAR" (note the quotes) is different from CHAR(1) in that it uses only one byte of storage and therefore can store only a single ASCII character. It's used in the system catalogs as a simplistic enumeration type.

Special character types

You can store a large character string in a CLOB type. CLOB is semantically equivalent to VARCHAR2 except you don't specify a length limit. Generally, use a CLOB type if you don't know the maximum string length.

The longest possible character string that you can store in a CLOB type is about 1GB.

Thus, use of the CLOB type is limited by what can be done for TEXT, such as a maximum size of approximately 1GB.

For 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.

• On this page
• Overview
• Example: Using the character types
• Special character types