Why not separate data?

While normalisation does indeed eliminate data duplication and drastically cut down on the chance of operator error, it does have some side effects. For example, to properly join two tables together to give one result is harder than a normal query, and much harder to optimise. It is also a little slower, because MySQL has to read from several places at once, rather than just one table. Of course, this second downside is negated entirely by the saving in space!


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