You may not need to read this chapter! Database management systems (DBMS) are very efficient, and if you have a modest amount of data, most of your queries will probably be carried out in the blink of an eye. Complicating your life in an attempt to make your queries a little faster does not make a great deal of sense. However, if you have (or might have) vast amounts of data and speed is absolutely critical, you will need more skill and experience than you are likely to get from reading one chapter in a beginners’ book. Having said that, you are likely to have people tell you that it matters how you express your queries or that you should be indexing your tables, so it is handy to have some idea about what is going on behind the scenes and understand some of the terminology.