WEBVTT 00:00.200 --> 00:03.170 This video we're going to answer a simple question. 00:03.450 --> 00:10.760 Back when we typed describe table names to describe cats What's up with this part. 00:10.960 --> 00:11.580 What is this. 00:11.590 --> 00:15.010 No column here in this little table. 00:15.010 --> 00:18.540 And why is there to is for name and age. 00:19.000 --> 00:20.500 So this video is all about. 00:20.520 --> 00:20.940 No. 00:20.980 --> 00:22.100 The concept of No. 00:22.240 --> 00:24.500 I've been working with no sequel. 00:24.820 --> 00:31.490 So to start off let's talk about what NO means NO basically means that the value is on known. 00:31.500 --> 00:36.430 It's sequels way of saying I don't know what this is or there is no specified value. 00:36.610 --> 00:39.570 An important note is that it does not mean zero. 00:39.670 --> 00:41.730 Some people often think no means zero. 00:41.730 --> 00:43.600 It doesn't in this context. 00:43.600 --> 00:48.910 So to illustrate the significance of these having a yes here it basically means that these are permitted 00:48.910 --> 00:49.960 to be No. 00:50.170 --> 00:54.780 It's OK if they have an unknown value and that's that happens by default. 00:54.790 --> 00:57.680 To illustrate though that that is the case. 00:57.960 --> 01:00.190 Here's a little bit of code right now. 01:00.220 --> 01:01.960 We could run this command. 01:02.290 --> 01:09.460 We have a catch table with name and age but we could do insert into cats and only specify a name. 01:09.520 --> 01:15.340 And in this case I used Alabama not sure who named her cat Alabama but you could probably say who names 01:15.340 --> 01:20.600 are cat blue which is what I named my cat so we could run this command. 01:20.610 --> 01:23.220 And Age has no specified value. 01:23.230 --> 01:25.750 So in fact let's try it right now. 01:25.810 --> 01:29.360 Make some space inserts into cats. 01:31.640 --> 01:33.010 Name. 01:34.600 --> 01:39.100 Values is the siren. 01:40.190 --> 01:49.740 Our Bama just like that we don't get any warnings or anything saying that name her that age is empty. 01:49.740 --> 01:50.830 Nothing like that. 01:51.060 --> 01:59.140 Now would you like star from cat you'll see that we have a new cat whose name is Alabama. 01:59.400 --> 02:00.810 But age is no. 02:01.050 --> 02:09.120 And again that's because we have no oil as a permitted value or it's technically not of value but age 02:09.150 --> 02:10.240 is allowed to be no. 02:10.350 --> 02:15.620 So his name so I could do the same thing or an even more extreme version. 02:15.720 --> 02:21.340 I could run this insert into cats nothing values nothing. 02:21.620 --> 02:32.190 You know if I did that take a moment to guess insert into cats nothing values nothing. 02:32.220 --> 02:33.640 What do you think will happen. 02:34.300 --> 02:36.280 Let's do a select star. 02:36.480 --> 02:40.230 Now we have cat no name no age no. 02:40.440 --> 02:43.050 So then the question becomes how do we prevent that. 02:43.050 --> 02:47.430 How do we require that name is not know and that age is not enough. 02:48.000 --> 02:51.800 And the answer is not no. 02:52.120 --> 02:59.080 So what we can do is specify when we actually define a table that something let's say a field like name 02:59.620 --> 03:00.770 is not all. 03:01.210 --> 03:03.070 And we use this syntax right here. 03:03.250 --> 03:11.250 So here's an example for a cat to table and I'll be using this convention Cat 2 Cat 3. 03:11.560 --> 03:19.160 So in a cat to table or 2.00 version when we define it we would say name is Vardar. 03:19.180 --> 03:24.760 This time I use 100 but the limit doesn't matter really followed by not no. 03:25.300 --> 03:29.280 So that means that it will not be permitted to be empty. 03:29.650 --> 03:34.990 And then age is also an IT age is an integer who is also not no. 03:35.590 --> 03:42.690 So if we try that right now I'm going to create a table Kappes too. 03:43.150 --> 03:53.820 And we're going to have and I'll do this on separate lines name is Vardar 100. 03:54.180 --> 03:54.920 It's OK. 03:55.000 --> 04:03.620 This one you can have longer names and then you have not know followed by age. 04:03.680 --> 04:10.320 Isn't it also not know what hit enter. 04:10.320 --> 04:22.390 Now let's start off by using describe cats to this time under no for both fields says no. 04:22.430 --> 04:26.200 So that's one way to tell that these are not allowed to be No. 04:26.540 --> 04:29.500 And just to emphasize this I made a slide. 04:29.540 --> 04:30.570 Notice the difference here. 04:30.710 --> 04:34.050 So now let's actually put it to the test. 04:34.100 --> 04:43.610 Let's try to insert into Cat 2 and this time will only do name and we'll leave off age and then we'll 04:43.610 --> 04:49.310 have values and name for this one will be Texas. 04:49.320 --> 04:51.960 In keeping with the state theme. 04:52.570 --> 04:53.400 OK. 04:54.050 --> 04:55.830 What do you think will happen. 04:55.940 --> 04:59.540 Insert into cats where age is not allowed. 04:59.600 --> 05:09.020 No but we're not specifying age so it says queery OK we didn't get an error message and we got a warning. 05:09.280 --> 05:12.730 So let's do show warnings warning field. 05:12.790 --> 05:15.340 Age doesn't have a default value. 05:15.610 --> 05:20.600 So what it's telling me is that I left age off I didn't specify it. 05:20.710 --> 05:22.600 So what it was going to do is make it no. 05:22.750 --> 05:25.120 But then no not allowed to be no. 05:25.240 --> 05:31.060 So I need to go find a default value and there's not a default value specified. 05:31.060 --> 05:37.220 So if we look you can probably guess her next or next video will be on default values. 05:37.330 --> 05:44.930 But if we do select star from Cat 2 you can see it automatically defined 0. 05:45.250 --> 05:50.620 So the next video we'll talk about why that happened but the way that it works if it's not allowed we 05:50.620 --> 05:53.650 know you don't have a default it's going to be zero. 05:53.650 --> 06:02.800 Now let's try the same thing with insert into Cat 2 and this time only age is specified and age will 06:02.800 --> 06:07.990 be 7 I get the same query OK. 06:07.990 --> 06:10.800 One morning show warnings. 06:11.290 --> 06:14.640 This time it says field name doesn't have a default value. 06:15.950 --> 06:17.720 Let's do our select star. 06:17.720 --> 06:20.800 Notice what we get right here earlier. 06:20.990 --> 06:22.780 See how far back I can go. 06:22.790 --> 06:24.140 We had no. 06:24.380 --> 06:30.040 1 we didn't specify a name when we inserted into cats just regular cats not cats too. 06:30.410 --> 06:33.830 But now when I don't specify a name it doesn't say no. 06:34.100 --> 06:36.090 And this is an empty string. 06:36.140 --> 06:37.520 So there's a difference. 06:37.520 --> 06:39.760 No means that there is no value at all. 06:39.770 --> 06:47.410 We didn't specify empty string is just a type of a VAR char that just has nothing in it. 06:47.690 --> 06:50.340 So you can think of it as this basically. 06:50.340 --> 06:54.260 OK so next we'll talk about how we specify these default values.