WEBVTT 00:00.090 --> 00:03.680 So next step we're moving on to the next subset of logical operators. 00:03.690 --> 00:09.240 There is a group that fits together nicely which you're probably familiar with just from middle school 00:09.240 --> 00:11.110 or early school years. 00:11.460 --> 00:17.160 And those are the greater than greater than an equal to or sorry greater than or equal to less than 00:17.400 --> 00:18.630 and less than or equal to. 00:18.780 --> 00:22.160 So four operators are very similar and pretty useful. 00:22.470 --> 00:29.700 So this is the greater than operator in my school it's pretty standard the way this is called Alligator 00:29.850 --> 00:30.550 bracket. 00:30.690 --> 00:34.120 I don't know what to call this honestly I just call it the grade with bracket. 00:34.140 --> 00:40.860 It's pretty universal across programming and it allows us to do things like select all the books released 00:40.950 --> 00:48.010 after a certain year so select all books where release is greater than the year 2000. 00:48.720 --> 00:50.460 And typically we're working with numbers. 00:50.460 --> 00:53.380 I'll talk about strings and a little bit but typically we're working with numbers. 00:53.490 --> 01:02.070 So an example earlier today I was looking on every NBA to book an Air B and B and they have a filter 01:02.070 --> 01:06.180 that allows you to set a minimum price or maximum price. 01:06.180 --> 01:11.940 So if I wanted to I could have gone in and said I only want to book you know every piece that have a 01:11.940 --> 01:17.130 price greater than $50 a night or something to filter out the $20 a night. 01:17.430 --> 01:21.590 You know couches and some person's living room so that's powered. 01:21.600 --> 01:24.300 Behind the scenes most likely by a greater than sign. 01:24.420 --> 01:28.480 So now let's give it a shot on our own over here. 01:28.860 --> 01:35.320 Let's start by just selecting all titles and released here from books. 01:35.760 --> 01:43.060 And let's just order by release here just ordering it will let us see you know when we remove things. 01:43.110 --> 01:45.950 It will make it clearer rather than having them just be jumbled. 01:46.430 --> 01:46.800 OK. 01:46.920 --> 01:52.980 So we've got 1945 up to 2017 if I want to go ahead and do what I showed you which is select all the 01:52.980 --> 01:57.580 books released in the 2000s or after the year 2000. 01:57.790 --> 02:10.190 All I need to do is add in where release to year is greater than 2000 just like that. 02:10.320 --> 02:12.750 And if we look we lost everything. 02:14.660 --> 02:16.520 From here on back. 02:16.520 --> 02:19.920 So from Cannery Row to The Amazing Adventures of Kavalier and Clay. 02:19.940 --> 02:23.420 Important to note that 2000 is not included. 02:23.480 --> 02:24.610 We'll get to in just a moment. 02:24.800 --> 02:26.950 But everything greater than 2000 is. 02:26.990 --> 02:33.170 So that gives us all loops it's just all these books for American Gods down to Lincoln and the Bardo 02:34.710 --> 02:36.670 you can see here we go. 02:37.230 --> 02:43.360 So that brings us to greater than or equal to which works exactly the same way except you add in this 02:43.390 --> 02:48.430 equal sign afterwards which makes it rather than greater than it makes it greater than or equal to which 02:48.430 --> 02:50.210 means that it's inclusive. 02:51.340 --> 02:57.220 So if I just change that and do where released year rather than greater than is greater than or equal 02:57.220 --> 03:02.760 to 2000 now it includes the year 2000. 03:02.770 --> 03:05.010 Let's do one more quick example. 03:05.350 --> 03:13.780 Let's do a select title and stock quantity from books and let's say that we're going to do a sale because 03:13.990 --> 03:16.980 we have some excess stock in some of our books. 03:17.060 --> 03:23.380 Any book that we have more than one hundred including one hundred Let's say so 100 or more copies in 03:23.380 --> 03:24.230 stock. 03:24.460 --> 03:27.150 We want to select and we're going to discount them. 03:27.520 --> 03:28.800 So how do we select those. 03:29.020 --> 03:30.430 Well it's pretty straightforward. 03:30.430 --> 03:36.940 We're just going to select title and stock quantity from books where stock quantity is greater than 03:37.570 --> 03:40.430 or equal to 100. 03:40.960 --> 03:42.100 And there we go. 03:42.190 --> 03:45.290 These are the books that we're going to discount. 03:45.420 --> 03:46.170 All right. 03:46.500 --> 03:46.850 OK. 03:46.860 --> 03:49.670 So there's one other small tangent I want to talk about. 03:49.950 --> 03:54.220 It's a bit of a diversion away from the tables and books that we've been working with. 03:54.240 --> 03:57.350 This has nothing to do with any particular data. 03:57.960 --> 04:05.360 But if you try running something like this select ninety nine greater than one what do you expect. 04:06.790 --> 04:10.310 Well go ahead and try to if you'd like to go and type it over here. 04:10.690 --> 04:18.050 Select ninety nine greater than one if we hit Enter we get the number one back. 04:18.070 --> 04:18.370 All right. 04:18.370 --> 04:23.490 So if you're familiar with other programming languages you've probably come across boolean values. 04:23.500 --> 04:25.020 True or false values. 04:25.270 --> 04:27.850 And that's what my ask who is replicating here. 04:28.000 --> 04:34.250 So the way that it works in Boolean logic is it actually works with the numbers zeros and one. 04:34.320 --> 04:39.990 So we know that ninety nine is greater than 1 that's true. 04:40.480 --> 04:44.290 So we get one which is equivalent to true. 04:44.400 --> 04:48.430 Basically this evaluates to one which you can think of as evaluating to true. 04:48.450 --> 04:50.280 So if it's if that's confusing you. 04:50.310 --> 04:51.410 Let's try something. 04:51.840 --> 04:53.380 Let's change nine. 04:53.610 --> 04:59.510 Greater than 1 2 is ninety nine greater than 5 6 7. 05:00.000 --> 05:00.800 I just lost it. 05:00.810 --> 05:01.430 Here we go. 05:01.710 --> 05:03.380 We know that that's false. 05:03.660 --> 05:06.030 And you can see if we get zero. 05:06.810 --> 05:08.290 So the reason I'm showing this to you. 05:08.330 --> 05:09.120 Well there's two reasons. 05:09.120 --> 05:14.010 One is that it will help us going forward with some of the other things are going to show you when we 05:14.010 --> 05:15.430 can start changing things together. 05:15.450 --> 05:20.640 You'll be able to evaluate them and kind of do some exercises on your own first. 05:20.760 --> 05:25.590 The other thing and the more important reason is that this is what's happening behind the scenes. 05:25.830 --> 05:29.370 When we have something like this right here we're stuck. 05:29.370 --> 05:31.730 Quantity is greater than or equal to 100. 05:31.740 --> 05:37.110 You can almost think of it as my as you're going through every stock quantity and playing it in here 05:38.130 --> 05:41.530 and trying OK it's 100 greater than or equal to 100. 05:41.790 --> 05:42.360 One. 05:42.480 --> 05:43.010 Yes. 05:43.080 --> 05:43.410 OK. 05:43.410 --> 05:47.170 So keep that one is 23 greater than or equal to 100. 05:47.260 --> 05:48.890 0 No false. 05:48.900 --> 05:54.630 So get rid of that one and if it does that you know going down the line that's kind of the humanised 05:54.630 --> 06:00.390 version if you will but it's evaluating to these numbers but those numbers are just you know bits and 06:00.390 --> 06:01.690 memory. 06:01.950 --> 06:03.870 But the concept is the same. 06:04.350 --> 06:08.770 So if you'd like let's wrap this up with just a really simple exercise. 06:09.000 --> 06:12.650 I'm going to type up a few things for you to evaluate them yourselves. 06:14.760 --> 06:15.180 OK. 06:15.200 --> 06:22.070 So I typed up a couple of examples here and I'd like for you to just either mentally try these or actually 06:22.070 --> 06:22.950 try them yourselves. 06:23.150 --> 06:27.010 And remember you'll need to actually run select and don't need a semi-colon. 06:27.040 --> 06:29.780 But what's the result that you expect. 06:30.110 --> 06:32.580 And there are a couple of straight forward ones. 06:32.660 --> 06:37.700 And then I threw in two string ones at the end basically to give myself a talking point at the end. 06:37.700 --> 06:43.760 I want to talk about why this happens and if you should care so go ahead I'll throw up the thing on 06:43.760 --> 06:45.640 the screen that says you should do it. 06:45.890 --> 06:48.150 And then in like two seconds I'll be back. 06:49.610 --> 06:51.300 All right I'm back. 06:51.300 --> 06:52.640 So first one. 06:52.690 --> 06:53.730 One hundred. 06:53.730 --> 06:54.710 Greater than five. 06:54.720 --> 06:55.640 Is that true. 06:55.890 --> 06:58.390 Well yes I believe that to be true. 06:58.470 --> 07:01.740 Just to double check it gives us one. 07:01.830 --> 07:06.050 That means we're in the clear negative 15 greater than 15. 07:06.050 --> 07:07.120 Is that true. 07:07.400 --> 07:11.440 Well no I don't think so. 07:11.640 --> 07:12.570 And we get zero. 07:12.980 --> 07:14.150 All right. 07:14.150 --> 07:17.530 Nine greater than negative 10. 07:17.630 --> 07:25.140 That seems like it should be true and it is what about 1 greater than 1. 07:25.430 --> 07:27.340 Well I don't think one is greater than one. 07:27.380 --> 07:28.450 So it's false. 07:28.460 --> 07:32.350 However if there was the equal sign of course it would be true. 07:33.200 --> 07:42.170 Now these two string comparisons with greater than less and is notorious in all languages for one being 07:42.200 --> 07:46.140 annoying and confusing and to differing radically between languages. 07:46.310 --> 07:51.860 So the advice that I would give to anyone is to just avoid ever having to do anything like this. 07:51.860 --> 07:55.320 There are ways around it but I just wanted to show you what happens. 07:55.340 --> 07:59.490 So what do you think is the lowercase a culture for B. 07:59.600 --> 08:01.850 So is it greater than or less than B. 08:02.570 --> 08:08.320 And in some languages it is greater than in others it's less than in my case my ass. 08:08.340 --> 08:17.610 Q Well if we hit Enter we can see that a is not greater than B meaning that it's less than B although 08:17.610 --> 08:22.300 technically that statement is logically wrong because it could be equal to B. 08:22.500 --> 08:26.560 But as you can see if I add that equal sign it's still false. 08:26.610 --> 08:29.650 So we know definitely a is less than B. 08:30.030 --> 08:36.800 Ok so that brings us to our last one which is a bit tricky upper case a greater than lower case. 08:37.230 --> 08:42.980 And if we run with a semi-colon you'll see that it's false. 08:43.080 --> 08:46.060 So uppercase case is not greater than lowercase J. 08:46.320 --> 08:53.850 So then does that mean that it's lower as upper case a come before lower case. 08:54.240 --> 08:59.420 And the answer is actually if we change this just slightly to be greater than or equal to. 09:00.000 --> 09:01.410 You'll see now it's true. 09:01.710 --> 09:08.150 So that tells us uppercase a is equivalent to lowercase say in my eyes. 09:08.340 --> 09:09.570 And we've seen that before. 09:09.750 --> 09:13.670 When we do something like Well let me just type it again. 09:13.750 --> 09:26.210 Select author L. name where author name equals Buju Eggers like this. 09:26.670 --> 09:33.000 And of course they add in the all important table name from books. 09:34.170 --> 09:35.410 So if I do this. 09:36.210 --> 09:41.130 And let's also do title just to make it easier to see what's going on. 09:41.130 --> 09:42.750 It matches just fine. 09:43.030 --> 09:46.700 But I can also do this with lowercase e and it works just the same. 09:46.800 --> 09:50.950 Or I can do Aggers like that with two uppercase G's. 09:50.970 --> 09:56.430 So the way that string comparisons work in my school is quite odd in and if you're familiar with other 09:56.430 --> 10:00.280 languages it's very different from pretty much every language I've worked with. 10:00.290 --> 10:03.670 So just something worth noting that case doesn't actually matter.