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Recordings of real interviews and useful information for preparation can be found on boosty https://boosty.to/vanyaio Go trainer for preparing for an interview: https://stepik.org/a/206788 Tasks on goroutines and Go channels for interviews: https://stepik.org/a/207625 Second video: How a B-TREE index in databases works • How a B-TREE index in databases works Third video: EXPLAIN in databases in 10 minutes • EXPLAIN in databases in 10 minutes 0:00 Slow query 0:55 What is an index, creating a simple index 1:55 Index over the primary key 2:55 Interview task in ozone 4:25 Composite indexes 7:52 Indexes and ORDER BY 9:40 Selecting indexes for a task 11:30 The order of columns in the index when equalities 12:10 Column selectivity 15:05 Comparing indices 20:30 Throwing out a non-selective column 22:50 Applying the theory 25:20 The importance of the nature of data 27:05 Partial indices 28:00 Final comparison 32:53 Conclusions