Choosing a Natural Key in .NET

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Choosing a Natural Key
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magine using mobile phone numbers as a natural key on a table of your friends it seems perfectly reasonable at first, because by their nature, the numbers are distinct. But not everyone has a cell phone; some people have more than one cell phone; and people change their numbers on occasion. You could be making a great deal of trouble for yourself down the road. If you have three tables in your database that reference a friend by her key, and the key is a phone number that has changed, you will have to write a script to update that value wherever it appears in the other tables.
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The ACID principle
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SQLite transactions are ACID atomic, consistent, isolated, and durable. This is an old principle in database design, and understanding how SQLite answers the problems of database design can give you some context as to just what sort of database SQLite is meant to be. Atomic means that the transaction either happens or it doesn t if an error occurs, your change rolls back without corrupting your data. You can visualize the transaction as something that happens instantaneously, and there is no way for an error to cause it to get stuck in the middle. SQLite transactions are even atomic if there is a power failure or a system crash!
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NOTE
It is no small feat to promise that a transaction will not corrupt your table even in the event of a power failure. A much-simplified explanation for how this is possible is that the centrifugal force of the hard disk makes your transaction cling in place; if the disk stops, the transaction goes flying off. Unfortunately, this explanation is oversimplified and doesn t make sense for a few reasons. You can find a real explanation from the engineers at www.sqlite.org/ac/atomiccommit.html.
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Consistent means that the transaction throws an error (and quits the transaction) if an illegal value is stored or a data conflict arises. Again, no corrupted tables are left behind. This ensures that a transaction is consistent; each transaction knows that the data in the table is valid before it starts working. An isolated transaction is a transaction that occurs at its own distinct time relative to other transactions. If you send two transactions at once, neither transaction sees the data in a half-edited state. SQLite achieves isolation by locking tables down while they are being acted on. An enterprise-level database doesn t have that luxury, because it has to support concurrency dozens of users interacting with the same data at the same time. This doesn t mean that concurrency isn t supported by SQLite, but it does mean that if you have more than a few hundred users acting on the same data at the same time, you are sure to see a performance loss as transactions queue up and wait for tables to unlock. Isolation is something that many database systems strive toward, but can never fully accomplish in order to preserve concurrency. Because SQLite uses table locking, the transactions are absolutely isolated without any risk, and even better, without a lot of code written to try to manage that risk. These are the principles of simplicity, stability, and lightness working in perfect harmony. Finally, durable means that once a transaction is completed and you ve been informed that it was successful, those changes are there to stay. This characteristic seems somewhat dubious; do you believe that there was a database engine in the past that was rolling back transactions for no apparent reason Maybe there was, but then again maybe they just needed a d.
Part III
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SQL is the language of choice for manipulating databases. It is really easy to find help on the SQL language, but keep in mind that each database engine has minor syntax differences. The database implementation in AIR supports most of the SQL-92 standard, which is exactly as old as it sounds, so much of the documentation you find online for SQL includes newer features not available in AIR. When in doubt, you should start with help for AIR and then look to help for SQLite. Basic SQL calls come in three phases: Creational Modification Retrieval Creational calls define the structure of your tables, so basically anything that changes what columns are available is a creational call. Modifications add or change data in your tables. Retrieval gets that data back out.
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