Welcome to Part 2 of Understanding Indexes. In Part 1 we talked about the magic that indexes bring to our data searches. They can make our data searches drastically faster. Now our simple little example we only had, what three, six nine names, I think there's nine names there. What if we had 9,000. Okay. You can see how indexes allow for these range searches to drastically speed up this process of finding records. But now let's take a look at kind of the dark side of indexes. Now no doubt about it everybody agrees indexes make retrieving records much, much faster because we can find those ranges, use those ranges and there's certain logic that we can deduce from than that and we can program that logic into our database management systems and find records very fast. But what do indexes do whenever we want to add or change a record? And now here's the dark side of indexes. Okay. So let's start off we'll take our same nine names and we're going to add Harry King to this list right here. Well this is a non-indexed list of names and I want to, I'm going to point out here some of the little tricks in databases that you can use just based on this aspect of indexes. Okay. Since these names aren't in any particular order we can add Harry King to this list very easily. Right. There he is, good old Harry goes on the very bottom of the list. Now if I'm running a database and let's say that I'm running a database for like a home shopping network where we flash something up on the TV screen and we want to sell as many genuine diamond necklaces for 9 dollars and 95 cents as we possibly we can. We want to take as many orders as we can in 15 minutes. I want to use a database that I can add names to the database table as quickly as possible. That means I may want to build a table with absolutely no indexes so I can just stick data in at the bottom. We'll worry about order later but for now let's just get the data in there as quickly as we can, that's one way to do it. Now let's take a look same list and let's look at adding Harry King to an indexed list. Alright. So here's our list and now notice that we've indexed it based on the last name. And so they're all and nice and neat in that order, Mary Ashton, George Cole, Arthur Hamilton, Frank Harris. Here's our three Ls that we looked for in Part 1. Now notice if we're going to add Harry King to this list H, I, J, K, H, I, J, K he's going to go right in here. Right. This is where Harry King would have to be inserted. So to add Harry King to this list we first have to move everybody down one and insert Harry King. Now think about that just a minute. The index had to be kind of modified a little bit and everybody from Bob Lane down had to be renumbered because Harry King changed the order from Bob Lane down, did he not? So there you see the problem of using indexes when you're going to be making a lot of inserts or modifications or even deletes. Think about this. What if Janet Langley got married and her name became Janet Armstrong? Well guess what? That's going to affect our index. Janet Langley is going to move from the Ls way up to the top, Armstrong, he's actually going to be the first name in our list. So what you'll find is if you have a lot of indexes on your tables and you make an insert, the insert's going to be slower. It's going to take it longer to go in or longer for that to complete because Access has got to make some notes somewhere in there about wait a minute, wait a minute this has changed the order. So now she's going to show up right here, these are other guys have got to move down one and so forth. I can change the way that I create my data or the way I populate my tables with some database products that will give me some blank space in there to help minimalize the effect of inserts update and deletes on indexes. But that's a much, much deeper topic. But I want you to understand all the implications of indexes and how it can affect how you use your database. Okay. So a lot of indexes make data retrieval much, much faster. But the flip side of that is, is it makes your inserts, update and deletes much, much slower because there's more maintenance has to be involved okay? So if you've got your head wrapped around Part 1 and Part 2 here trust me you're way down the road with your database design and administration features because this is a concept that's fundamental to understanding how your database is being used and whether indexes will really help you or hurt you in the long run. So this is a quick look at understanding some basic things about indexes.
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