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I am designing a database in Mysql which will be filled with quite large amounts of raw data. I wanna know that I should define indexes before I insert the data, or I should first insert my data and then create the index? is there any difference?
Also I wanna know If I have wanna have index on 2 columns, is it better to index them separately or together?
Thanks
If you are doing a bulk load, my opinion is to not have indexes up front, that will slow the load to constantly write index pages, especially if a larger data set. That being said, after the tables are populated, do a SINGLE statement to build ALL the indexes you expect instead of one-by-one. I learned the hard way a long time ago. I had a table of 14+ million rows and had to build 15+ indexes. Each index was increasingly longer than the last. It appeared each time a new index, it needed to rebuild the pages for the prior. Doing them all at once proved significantly better.
As for multiple column indexes… it depends on how your querying will be performed. If many queries WILL utilize a pair or more of columns in the WHERE condition, then yes, use multiple columns in a single index.