By Richard Stones, Neil Matthew
This is not particularly a foul e-book, yet given the readability with which PostgreSQL's authentic (and loose) documentation is written, loads of it additionally isn't really valuable. convinced, it truly is quite thick, yet loads of these pages are devoted to fairly grotesque screenshots and Windows-specific silliness i am keen to wager few contributors of this product's audience are quite drawn to. There also are complete chapters devoted to C# and Java APIs which should still most likely be separate books in the event that they fairly desired to do justice to such topics--their inclusion the following simply seems like unnecessary filler.
If you've got totally no thought what SQL is and wish to get your toes rainy with Postgres, then this can be the absolute booklet for you. when you have a high-quality thought what you are doing and simply are looking to decide up on a few of Postgres' quirks, i am not too certain you may be getting your money's worthy the following. It simply attempts to hide approach an excessive amount of flooring too fast, and the data finally ends up getting stretched a bit skinny.
Read or Download Beginning Databases with PostgreSQL: From Novice to Professional, Second Edition (Beginning from Novice to Professional) (Volume 0) PDF
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Extra resources for Beginning Databases with PostgreSQL: From Novice to Professional, Second Edition (Beginning from Novice to Professional) (Volume 0)
Adding Information So far, all we have looked at is our database emulating a single worksheet in a spreadsheet, and we’ve just touched the surface of SQL’s features. As we will see in this book, however, relational databases such as PostgreSQL are very rich in useful features, which take them well beyond the realms of spreadsheet capabilities. One of the most important capabilities of databases is their ability to link data together across tables, and that is what we will look at now. Using Multiple Tables Recall our customer order problem, where our simple customer spreadsheet suddenly became very untidy once additional order information was stored for each customer.
There is obviously no need to store all the customer details again. We already know that given a customer_id, we can find all the details of that customer in the customer table. You might be wondering why we’ve omitted the details of what was ordered. Certainly, that is an important aspect of orders to most customers—they like to get what they ordered. If you’re thinking that it’s a similar problem to not knowing in advance how many orders a customer will place, you’re quite right. We have no idea how many items will be on each order.
At this point, you might suggest using a combination of name and phone number. Certainly, it’s unlikely that two customers will have both the same name and the same phone number, but quite apart from being inelegant, another problem is lurking. What happens if a customer changes to a new phone provider and subsequently the phone number changes? By our definition, a unique customer must then be a new customer, because it is different from the customer we had before. Of course, we know that it is the same customer, with a new phone number.