[mattmanser]

intermediate/advanced

Know that most databases can spit out a "worst performing queries" and "overall most expensive" reports. The method varies per engine. Always illuminating, and usually not the queries you were expecting.

Know how to turn logging on/off and where the logs go.

Know there are a bunch of system tables that keep data about all your tables in it in most engines, information_schema tables. Rows, size, columns, etc. These are actually defined in the SQL spec, but various SQL vendors have even more available, e.g. there's a load of extra stored procedures in SQL Server.

Be able to generate and read a query plan report for your engine, which will tell you what's causing a slow query.