For small numbers of rows requiring updates, it can be adequate to use an UPDATE statement for each row that requires an update.But if there are a large number of rows that require an update, then the overhead of issuing large numbers of UPDATE statements can result in the operation as a whole taking a long time to complete.The traditional advice for improving performance for multiple UPDATE statements is to “prepare” the required query once, and then “execute” the prepared query once for each row requiring an update.But in many cases this only provides a modest improvement as each UPDATE operation still requires a round-trip communication with the database server.
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Second, the SET clause specifies which column that you want to modify and the new values.
To update multiple columns, you use a list comma-separated assignments.
My SQL UPDATE using NULL My SQL UPDATE command can be used to update a column value to NULL by setting column_name = NULL, where column_name is the name of the column to be updated.
The following My SQL statement will update pub_lang column with NULL if purch_price is more than 50.