I can very easily come back and edit my relationships, or change the relationships, by any time I'd like, going back to the Database Tools Tab, and just clicking on Relationships. So notice that if I've created this relationship, and I close it out, and save it, then that relationship, I can't see anything out here amongst the table information about it, but anytime I go back to Database Tools and Relationships, I will see all the relationships in my database between all my tables right here. Now what I want to do in this video, is talk to you about the options and editing these things, because again, over the course of time, your database is going to evolve as your data storage needs evolve, as your company evolves, your reporting needs revolve, and all that other stuff. Everything's evolving right? Well anytime I come back into this Relationship View, notice I can click on the relationship between these two tables and it will kind of become bold, then I can just double click it, and I can go right back to my Edit Relationships window here. Now you'll notice that I can easily change my connected columns just by choosing the drop downs here. I don't want to do that now, because it will my mess up my relationships, but I want to show you a couple of things, some of these may not make sense right now, but trust me when the time comes, this will kind of tickle your brain a little bit, and you will say, I remember that clown and that course, telling me that this could happen, and where was that? OK? First of all, we told it to enforce referential integrity, now that what it is doing, let me just cancel this for a second. This is making sure that I can't put, an, an entry in the students table, unless there is an associated IID in the instructor table OK? And so what I'm going to do here, is, I will close this out, and I will go to the students table, and I'm going to insert some data alright? So we're going to put in student number two, and we're going to say that we want to put an IID of two in here. Now this will be Frank Smith, and Frank Smith is fourteen years old, we don't do address and all that. Notice our default TN is here, remember let me just try to go to the next line, it says you have to put a value in the phone field, remember that? We made that required, so I'll come in here and I'll do 615887 it's amazing how I know these numbers isn't it? And so what I'm going to do now, is come back here, and try to click on the next line, and notice, it says, wait a minute dude, you can't add or change a record, because a related table is required in the instructor table. Well I'll say OK. Now notice I tried to put in an IID of two, an instructor ID of two, but if I go to the instructor table, and I can double click here to see this, I don't have an IID of two OK? So that is not going to work, and it caught me on that, and it said, wait a minute, you don't have a field to relate to over there OK? So let me close this out. Now anytime you put something in here that won't work and you can't change it, just hit the X, it's going to squawk at you, say OK, and then it's going to say with those irritating noises, do you want to close the database object anyway? The changes I've just made will be lost, yeah just get rid of them. Now let's go back to our Database Tools, and our Relationships, and let me go point out one thing. Double click again. Under enforced referential integrity which is working, by the way, I can choose to cascade update related fields and or delete related fields. What this means is, if I delete a row in a table, and it has a relationship to another table, it's going to say, do you want to reach into that table, and delete any related records. You'll have to think this through, and test it. Same thing for updates. Sometimes you want it, sometimes you don't. The hard and fast rule is you must figure it out at the time OK? Now one other thing, Join Types. Just remember that I told you this, I don't want to go too deeply here, but notice, by default, it's only going to include rows where the join fields from both tables are equal. Now we can do what's called a Left Join, and a Right Join, depending on where your tables are, and in this instance, we can include all records from instructor, and only those from students where the Join Fields are equal, and then we can switch it. This would be, notice I can't see it now, but notice students over here on the right, so it would be a right table, instructors on the left, it would be our left table, and it's, we're pulling all from instructor, that would be Left Outer Join, and all from students would be a Right Outer Join if you know your SQL stuff. If you don't, don't worry about it, just remember, if you ever need to tweak that, that's how you do it right there alright? And that's pretty much it. Be careful with setting up your relationships, and if you don't get this one to many or one to one like you want to see it, then think to go back out, and kind of tweak up your indexes on the column that you're joining on. And so we'll stop right there. Relationships can be tricky. Anytime you're having a problem with them, they're not doing what you intended them to do, or they're not setting up properly, go back out, look at those indexes, think it through, and test these things. Note we still haven't put data in our tables. We want to put our relationships in place first, test them with one or two lines of data, then delete that data out, and put your real data in. That's the way I always do it, that's the way a lot of people that I've worked with do it. Figure out what works best for you, follow the logic through, but the main thing is, you want to make sure that you have the proper data, related correctly, in your tables.
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