You should use this more as a reference than as an absolute measure. You can see the cost listed next to the number of rows-higher numbers mean longer run time. Then, the database will scan 600 rows (this is an approximate number). So this shows that the WHERE clause, which limits the date range, will be executed first. The entry at the bottom of the list is executed first. It's called the Query Plan, and it shows the order in which your query will be executed:
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For example, if you've got time series data, limiting to a small time window can make your queries run much more quickly: SELECT * How you do this will depend entirely on the problem you're trying to solve. Reducing table sizeįiltering the data to include only the observations you need can dramatically improve query speed.
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In this lesson, you'll learn to identify when your queries can be improved, and how to improve them. The lesson on subqueries introduced the idea that you can sometimes create the same desired result set with a faster-running query. Starting here? This lesson is part of a full-length tutorial in using SQL for Data Analysis.