How to prepend a string to a column value in MySQL?

I need a SQL update statement for updating a particular field of all the rows with a string "test" to be added in the front of the existing value.

For example, if the existing value is "try" it should become "testtry".

You can use the CONCAT function to do that:

UPDATE tbl SET col=CONCAT('test',col);

If you want to get cleverer and only update columns which don't already have test prepended, try

UPDATE tbl SET col=CONCAT('test',col)
WHERE col NOT LIKE 'test%';

UPDATE tablename SET fieldname = CONCAT("test", fieldname) [WHERE ...]

Many string update functions in MySQL seems to be working like this: If one argument is null, then concatenation or other functions return null too. So, to update a field with null value, first set it to a non-null value, such as ''

For example:

update table set field='' where field is null;
update table set field=concat(field,' append');