MySQL supports hexadecimal values, written using X'val', x'val', or 0xval format, where val contains hexadecimal digits (0..9, A..F). Lettercase of the digits does not matter. For values written using X'val' or x'val' format, val must contain an even number of digits. For values written using 0xval syntax, values that contain an odd number of digits are treated as having an extra leading 0. For example, 0x0a and 0xaaa are interpreted as 0x0a and 0x0aaa.

In numeric contexts, hexadecimal values act like integers (64-bit precision). In string contexts, they act like binary strings, where each pair of hex digits is converted to a character:

mysql> SELECT X'4D7953514C';
        -> 'MySQL'
mysql> SELECT 0x0a+0;
        -> 10
mysql> SELECT 0x5061756c;
        -> 'Paul'

In MySQL 4.1 (and in MySQL 4.0 when using the --new option), the default type of a hexadecimal value is a string. If you want to ensure that the value is treated as a number, you can use CAST(... AS UNSIGNED):

mysql> SELECT 0x41, CAST(0x41 AS UNSIGNED);
        -> 'A', 65

The X'hexstring' syntax is new in 4.0 and is based on standard SQL. The 0x syntax is based on ODBC. Hexadecimal strings are often used by ODBC to supply values for BLOB columns.

Beginning with MySQL 4.0.1, you can convert a string or a number to a string in hexadecimal format with the HEX() function:

mysql> SELECT HEX('cat');
        -> '636174'
mysql> SELECT 0x636174;
        -> 'cat'