Updating multiple values

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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.

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If you update a column that has been declared , an error occurs if strict SQL mode is enabled; otherwise, the column is set to the implicit default value for the column data type and the warning count is incremented.In the case where the application server and database server are on different hosts, the round-trip will involve network latency as well.The dominant factor in the time taken to complete the overall operation tends to be the “admin” work in conveying the application’s intention to the database server rather than the actual updates to the database.If you access a column from the table to be updated in an expression, assignments are generally evaluated from left to right.For multiple-table updates, there is no guarantee that assignments are carried out in any particular order.

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