I was talking with a few people about a query such as select * from table order by X, Y, Z limit G; > > As the "ORDER BY" for me could change to any number of 12 values in any order I am not able to use a multicolumn index as such I was looking at how to optimize in such case where sorting is dynamic.
On my dataset the query takes ~7 seconds for a full table scan but only .3 seconds when using the column index and returns ~80,000 records for the query (before the LIMIT) I was wondering if there is any reason that the order by syntax doesn't use the following logic, I was thinking of looking at the code but was told such a simple optimization must have a reason that its not already in the code, so I am asking here before I spend hours being stupid. This logic block will be based on the above query. 1. If index exists for column X and there is a limit on the query then use the index and sort the list, then return the first G values, continue past G until you hit a different value for X then the value that was at G 2. Use this smaller subset of data for then ordering the data based on Y 3. Order the data again based on Z 4. Return the sorted data like normal If there is a reason this optimization isn't in the code please someone let me know, if not I think I will take a look at adding it. -Botanic
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