Updating multiple fields mysql


07-Mar-2017 23:40

updating multiple fields mysql-51

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So, given a list of updates to apply we could effect them using the following steps: So in the example above we can reduce five statements to four. But now the number of statements is no longer directly dependent on the number of rows requiring updates.Even if we wanted to update a thousand rows with different values, we could still do it with four statements.In this case there are two distinct values, so we can do it in two UPDATE statements: So we can reduce the number of queries from five to two. But the extent to which this helps us reduces as the proportion of distinct SET values goes up.Eventually every SET value is different, for example: UPDATE staff SET salary = 1125 WHERE name = ' Bob'; UPDATE staff SET salary = 1200 WHERE name = ' Jane'; UPDATE staff SET salary = 1100 WHERE name = ' Frank'; UPDATE staff SET salary = 1175 WHERE name = ' Susan'; UPDATE staff SET salary = 1150 WHERE name = ' John'; Since every SET clause is now different, we can’t coalesce any queries using the approaches mentioned before, so we still have one UPDATE statement for every row requiring changes. What if we had a database table which contained a representation of the updates we wanted to make, e.g.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.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.

updating multiple fields mysql-23

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The ‘set’ parameter takes a Hash Ref whose keys are the columns to be updated.

But in many cases this only provides a modest improvement as each UPDATE operation still requires a round-trip communication with the database server.



Found a solution mysql UPDATE table SET last_update=now, last_monitor=last_update WHERE id=1;. I found this in MySQL Docs and after a few tests it works the following statement sets col2 to the current updated col1 value, not the original col1 value. The result is that col1 and col2 have the same.… continue reading »


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Sep 9, 2017. MySQL UPDATE command can be used to update multiple columns by specifying a comma separated list of column_name = new_value. Where column_name is the name of the column to be updated and new_value is the new value with which the column will be updated. The following MySQL statement.… continue reading »


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