Mysql updating multiple tables 100 minimal dating site
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.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.
“Bob Jones” appears in both companies, so we need to be careful to identify the company, but we don’t want to have to specify it repeatedly for each row.
So is structured so that approaches which are generic across different SQL databases are expressed in a base class, and approaches which only work for specific SQL databases are expressed in a subclass.
An object of the relevant class is instantiated when the call is made, and control then passed to the implementation relevant to the database in use.
So if the caller has a Postgre SQL database, and calls with data to represent our third example (where the target values are all unique), then the Postgre SQL-specific subclass will effect the updates using the table / UPDATE … To match on names we now need to match on two columns.
So whereas previously we specified the matching column using a scalar, when there is more than one column to match, we use an Array Ref.