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To update a table in MySQL using a select statement from the same table, you can use a subquery in the UPDATE statement. Here's an example:

UPDATE tablename SET column1 = newvalue WHERE id IN (SELECT id FROM tablename WHERE somecondition);

In this example, tablename is the name of the table you want to update, column1 is the name of the column you want to update, newvalue is the new value you want to set for the column, and some_condition is the condition that the rows you want to update should meet.

The subquery in the WHERE clause selects the rows that meet the condition, and the outer query updates the column1 with the new value for those rows.

Note: Be careful when using subqueries to update a table, as they can sometimes result in unexpected results or performance issues. It's important to test your queries thoroughly before running them on production data.