The UPDATE statement updates columns in existing table rows with new values.
The SET clause indicates which columns to modify and the values
they should be given.  The WHERE clause, if given, specifies
which rows should be updated.  Otherwise, all rows are updated. If the
ORDER BY clause is specified, the rows will be updated in the
order that is specified. The LIMIT clause places a limit on the number
of rows that can be updated.

The UPDATE statement supports the following modifiers:


 --- If you specify the LOW_PRIORITY keyword, execution of the
UPDATE is delayed until no other clients are reading from the table.

 --- If you specify the IGNORE keyword, the update statement will not
abort even if duplicate-key errors occur during the update.  Rows for which
conflicts occur are not updated.
