Updating databases in

Let us start with a simple table: UPDATE staff SET salary = 1200 WHERE name = ' Bob'; UPDATE staff SET salary = 1200 WHERE name = ' Jane'; UPDATE staff SET salary = 1200 WHERE name = ' Frank'; UPDATE staff SET salary = 1200 WHERE name = ' Susan'; UPDATE staff SET salary = 1200 WHERE name = ' John'; UPDATE staff SET salary = 1200 WHERE name = ' Bob'; UPDATE staff SET salary = 1250 WHERE name = ' Jane'; UPDATE staff SET salary = 1200 WHERE name = ' Frank'; UPDATE staff SET salary = 1250 WHERE name = ' Susan'; UPDATE staff SET salary = 1200 WHERE name = ' John'; We are no longer setting all the salary fields to the same value, so we can’t collapse it into a single statement.

But we can group the updates according to the value being set, and then do one UPDATE statement per distinct value.

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.

For information about entering new data in a database, see the article Add one or more records to a database.

Read this section if you are new to Access or unfamiliar with the concepts behind relational databases.

A more effective solution to this problem is to attempt to reduce the number of UPDATE statements.

A requirement arises in many systems to update multiple SQL database rows.

For small numbers of rows requiring updates, it can be adequate to use an UPDATE statement for each row that requires an update.

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