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9348827
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2012-02-19T11:42:17.393
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2012-02-19T11:42:17.393
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I think you're confusing the difference between a foreign key constraint and a check constraint. A foreign key constraint is there to enforce referential integrity and a check constraint constrains a column to containing only valid data. In your case this may seem like a minor difference but if we abstract it slightly I hope to make it clearer. If we consider a table <code>users</code> with the columns <code>user_id, user_name, address_id, join_date, active, last_active_month</code>; I recognise that this is not necessarily the best way of doing things but it'll serve for the point I'm trying to make. In this case it's patently ridiculous to have <code>address_id</code> as a constraint. This column could have any number of values. However, <code>active</code>, assuming we want a boolean <code>y/n</code> can only have two possible values and <code>last_active_month</code> can only have 12 possible values. In both these cases it's completely ridiculous to have a foreign key. There are only a certain number of values and by the definition of the data you are including these values cannot change. In your case, while you could go for a check constraint, unless you can be absolutely certain that the number of <code>actions</code> will never change a foreign key is the correct way to go. <hr> On a slightly separate matter, and as @pst mentioned, I see you've been eaten by the surrogate key monster. While this can result in performance improvements, in a table of the size you're envisaging ( 3 values, <code>insert / update / delete</code> ) or even a larger one all it serves to do is obscure what you're trying to achieve. It's not easy to look at <pre><code>ID Action System 1 1 1 2 2 1 </code></pre> and see what's going on, but: <pre><code>ID Action System 1 insert 1 2 update 1 </code></pre> is far easier to read; you may also want to consider doing the same for the <code>system</code> column - I probably would, though the number of possible values jumps slightly in this. Just my personal thoughts on the matter...
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1. POForeign key vs check constraint for integrity
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