changing all values in a mysql table

[LanceT]

Lets say in one of my rows a certain column  has the value "hello"

How do I change all of them to "hello world" without doing it manually?

Thanks.

[fenway]

Well, a simple UPDATE table SET value = 'hello world' WHERE value = 'hello will work...

[Barand]

I couldn't tell from that question whether to

change all the columns in the one row containing "hello" to "hello world"

or

change that certain column in all rows to "hello world"