Mysql updating multiple tables
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.
(It will use placeholders and parameter binding if it thinks it’s appropriate.) If given our second example with two distinct values, will spot that there are two distinct values, 12, and will effect this with two UPDATE statements as described above.
Optimising the number of UPDATEs by grouping the distinct SET values can be done in a way which is compatible with most common SQL databases. FROM approach requires knowledge of the specific SQL database being used.
and we could persuade the database server to apply those updates to the target table?
This is in fact entirely possible in many database systems.
A requirement arises in many systems to update multiple SQL database rows.
The ‘set’ parameter takes a Hash Ref whose keys are the columns to be updated.“value_columns” specifies the columns which will be updated (using SET). The second element provides the value to be SET in the column specified by “value_columns”.In this case, will spot that the target values are all 1200, and will effect the desired changes using a single UPDATE statement as described above.In the case of Postgre SQL, it can be done using a FROM clause with UPDATE, like this: This does an INNER JOIN between the tables “staff” and “updates” where the column “name” matches.The SET clause then takes the “salary” field from the “updates” table and uses it to update the “salary” field of the “staff” table.