CHAR

This article covers the CHAR data type. See CHAR Function for the function.

Syntax

[NATIONAL] CHAR[(M)] [CHARACTER SET charset_name] [COLLATE collation_name]

Description

A fixed-length string that is always right-padded with spaces to the specified length when stored. M represents the column length in characters. The range of M is 0 to 255. If M is omitted, the length is 1.

CHAR(0) columns can contain 2 values: an empty string or NULL. Such columns cannot be part of an index. The CONNECT storage engine does not support CHAR(0).

Note: Trailing spaces are removed when CHAR values are retrieved unless the PAD_CHAR_TO_FULL_LENGTH SQL mode is enabled.

If a unique index consists of a column where trailing pad characters are stripped or ignored, inserts into that column where values differ only by the number of trailing pad characters will result in a duplicate-key error.

Examples

Trailing spaces:

CREATE TABLE strtest (c CHAR(10));
INSERT INTO strtest VALUES('Maria   ');

SELECT c='Maria',c='Maria   ' FROM strtest;
+-----------+--------------+
| c='Maria' | c='Maria   ' |
+-----------+--------------+
|         1 |            1 |
+-----------+--------------+

SELECT c LIKE 'Maria',c LIKE 'Maria   ' FROM strtest;
+----------------+-------------------+
| c LIKE 'Maria' | c LIKE 'Maria   ' |
+----------------+-------------------+
|              1 |                 0 |
+----------------+-------------------+

Example of CHAR:

CREATE TABLE char_example (
   description VARCHAR(20),
   example CHAR(255)
) DEFAULT CHARSET=latin1; -- One byte per char makes the examples clearer

INSERT INTO char_example VALUES
   ('Normal foo', 'foo'),
   ('Trailing spaces foo', 'foo      '),
   ('NULLed', NULL),
   ('Empty', ''),
   ('Maximum', RPAD('', 255, 'x'));

SELECT description, LENGTH(example) AS length
   FROM char_example;

+---------------------+--------+
| description         | length |
+---------------------+--------+
| Normal foo          |      3 |
| Trailing spaces foo |      3 |
| NULLed              |   NULL |
| Empty               |      0 |
| Maximum             |    255 |
+---------------------+--------+

Data Too Long

When SQL_MODE is strict (the default) a value is considered "too long" when its length exceeds the size of the data type, and an error is generated.

Example of data too long behavior for CHAR:

TRUNCATE char_example;

INSERT INTO char_example VALUES
   ('Overflow', RPAD('', 256, 'x'));

ERROR 1406 (22001): Data too long for column 'example' at row 1

NO PAD Collations

NO PAD collations regard trailing spaces as normal characters. You can get a list of all NO PAD collations by querying the Information Schema Collations table, for example:

SELECT collation_name FROM information_schema.collations 
  WHERE collation_name LIKE "%nopad%";  
+------------------------------+
| collation_name               |
+------------------------------+
| big5_chinese_nopad_ci        |
| big5_nopad_bin               |
...

See Also

• CHAR Function

• VARCHAR

• BINARY

• Data Type Storage Requirements

_{This page is licensed: GPLv2, originally from fill_help_tables.sql}