This MySQL function converts hexadecimal numbers to their character equivalents.
Below is the syntax for this command. Text within square brackets (i.e, [ and ] ) are optional. Choices are separated by bars (i.e, | ). Ellipses preceded by a comma indicates a repeating pattern. Ellipses before or after syntax are used to highlight a relevant except from the larger syntax. Text displayed in italic letters represent text that should be replaced with the specific names related to the database (e.g., column with the name of the column).
This function converts hexadecimal numbers to their character equivalents. It reverses the results of the HEX() function and is available as of version 4.1.2 of MySQL.
To illustrate its use, suppose that in a table we have a column with a binary character in the data: specifically, tabs were entered through a web interface using an API. However, the column is a VARCHAR data type. The problem is that when the data is retrieved, we want to line up all the results in our display by counting the length of each column, and a tab keeps the display from lining up vertically. So we want to fix the data. We can use UNHEX() to locate rows containing the binary character and then replace it with spaces instead:
UPDATE students SET comments = REPLACE(comments, UNHEX(09), SPACE(4)) WHERE LOCATE(UNHEX(09), comments);
We've looked on an ASCII chart and seen that a tab is represented by the hexidecimal number 09. Knowing that bit of information, in the WHERE clause we're passing that value to UNHEX() to return the binary character for a tab, yielding the search string with which LOCATE() will search the column comments. If it doesn't find a tab in the column for a row, it will return 0. Those rows will not be included in the search results. The ones that do contain tabs will have a value of 1 or greater and therefore will be included in the results. Using UNHEX() along with REPLACE() in the SET clause, we replace all tabs found with four spaces.