Question

I have a table with data relating to several moments in time that I have to keep updated. To save space and time, however, each row in my table refers to a given day and hourly and quarter-hourly data for that day are scattered throughout the several columns in that same row. When updating the data for a particular moment in time I, therefore, must choose the column that has to be be updated through some programming logic in my PL/SQL procedures and functions.

Is there a way to dynamically choose the column or columns involved in an update/merge operation without having to assemble the query string anew every time? Performance is a concern and the throughput must be high, so I can’t do anything that would perform poorly.

Edit: I am aware of normalization issues. However I still would like to know a good way for choosing the columns to be updated/merged dynamically and programatically.

Answer 1

The only way to dynamically choose what column or columns to use for a DML statement is to use dynamic SQL. And the only way to use dynamic SQL is to generate a SQL statement that can then be prepared and executed. Of course, you can assemble the string in a more or less efficient manner, you can potentially parse the statement once and execute it multiple times, etc. in order to minimize the expense of using dynamic SQL. But using dynamic SQL that performs close to what you’d get with static SQL requires quite a bit more work.

I’d echo Ben’s point– it doesn’t appear that you are saving time by structuring your table this way. You’ll likely get much better performance by normalizing the table properly. I’m not sure what space you believe you are saving but I would tend to doubt that denormalizing your table structure is going to save you much if anything in terms of space.