Whenever I do a round of interviewing for a developer position one of the things I find is that many people do not have a firm grasp of database indexes, specifically SQL Server indexes (since that is what we use).
I'm probably the furthest thing from a DB guru, and many teams have dedicated DBA's who handle all that stuff, but I believe it's important for developers to have a strong understanding of how databases work as that's often the single point of failure.
SQL Server Central has a recent introductory article on indexes that is a very worthwhile read that I encourage you to have everyone you know read.
"Clustered indexes define the logical order of the table. The leaf level of the clustered index has the actual data pages of the table. Because of this there can only be one clustered index per table. A table that does not have a clustered index is referred to as a heap."
Read the full article
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