The function releases all previous memory or file resources associated with the variable and sets the file length to zero. The function does not write the current value of the BLOB variable to the file upon making the association. However, future changes to the variable, such as reading from a database into the variable, write the value of the variable to the associated file.
To save an existing value of the BLOB variable into a file, use the updateBlobToFile() system function, which does not use a temp file.