WEBVTT 00:07.940 --> 00:11.630 Okay, so in the previous lecture we dropped a primary key. 00:11.630 --> 00:14.000 And now we want to add a primary key back. 00:14.000 --> 00:17.510 Because if you go under student ID the bit ends. 00:17.540 --> 00:21.890 There is nothing like a P key which is the primary key. 00:21.920 --> 00:23.390 We have dropped it. 00:23.420 --> 00:28.640 Now if I should go ahead and add this primary key, I'm going to get an error. 00:28.640 --> 00:32.990 If I should go straight and do that from back, then go ahead and show you how to add a permanent key. 00:33.020 --> 00:36.440 And we want to see other table. 00:36.920 --> 00:40.820 And I want to alter either the students table. 00:42.200 --> 00:43.820 So alter table students. 00:43.850 --> 00:49.190 Then go ahead and add the primary key. 00:49.670 --> 00:50.090 All right. 00:50.120 --> 01:00.830 Now I'm going to add that to students underscore ID you can actually add this primary key to any of 01:00.830 --> 01:04.720 these columns so we can add to multiple columns for Y. 01:04.750 --> 01:13.990 I just want these to be here is because I just want that to just be for the stress ID. 01:14.200 --> 01:21.940 You can add that to maybe email or you add that to first name, last name, or because people are going 01:21.940 --> 01:25.120 to have exactly the same first name or last name. 01:25.150 --> 01:29.170 Yes, some two or more pieces can have exactly the same first name and last name. 01:29.170 --> 01:32.710 It happens, but they can't have the same email address. 01:33.430 --> 01:34.090 Yes. 01:34.090 --> 01:40.000 So it can also add email address to also be a primary key. 01:40.420 --> 01:42.430 But there's a problem right in here. 01:42.460 --> 01:50.530 If I should go ahead and uh, actually put a semicolon at the end of this and try to create this primary 01:50.560 --> 01:52.570 key, I'm going to run into a problem. 01:52.570 --> 01:53.020 Let me go ahead. 01:53.020 --> 02:01.570 I show you that it says the stress ID is duplicate could not create a unique index stress ID because 02:01.570 --> 02:02.180 Perimeter. 02:02.180 --> 02:09.290 We have the two people still there and that is don't go ahead and check them out. 02:10.730 --> 02:13.880 If we go ahead and check out these, we still have these two guys here. 02:13.910 --> 02:19.430 So first of all we need to delete these two people from here so we can be able to add our primary key. 02:19.430 --> 02:26.390 And to do that we go ahead and use the delete key word from the students table. 02:26.960 --> 02:30.320 So delete from students. 02:30.890 --> 02:36.500 Uh we have the ID or we are the students. 02:36.530 --> 02:39.830 Underscore ID is equal to one. 02:39.830 --> 02:44.390 And put a semicolon at the end of it and underscore here and is equal to square. 02:44.390 --> 02:45.020 And check it out. 02:45.050 --> 02:49.880 So we deleted two of them and they are gone right now. 02:49.910 --> 02:58.730 I can also go ahead and then put back our primary key a warhead and the other the table. 03:00.830 --> 03:08.320 So alter table and the table is a day student so terrible. 03:08.320 --> 03:12.130 Students are ahead and are at the. 03:13.120 --> 03:14.260 Primary key. 03:15.370 --> 03:16.990 So at primary key. 03:16.990 --> 03:20.680 And now we're going to add that primary key to. 03:21.400 --> 03:27.280 The students underscore ID the input is semicolon at the end of it. 03:27.670 --> 03:30.700 Now we can go ahead and execute this query and check it out. 03:30.700 --> 03:32.590 So our table. 03:32.620 --> 03:44.080 Now if I should go ahead and uh select all from students and put a semicolon at the end. 03:44.260 --> 03:45.640 Let's go ahead and check it out. 03:45.640 --> 03:48.610 So you can see that the primary key is back. 03:49.060 --> 03:52.510 And we have deleted one of these, uh, students. 03:52.510 --> 03:57.340 And our table is now 999 out of 999. 03:57.460 --> 04:02.470 Let's go ahead and, uh, add back the student. 04:02.650 --> 04:06.000 Let's go ahead and put in this back again. 04:06.000 --> 04:10.650 So this is what we copied from the coach studio. 04:10.680 --> 04:12.990 Uh, studio code, which will have right in here. 04:12.990 --> 04:15.000 So I'm going to put this back again. 04:15.000 --> 04:23.490 But, uh, right now we go ahead and, uh, set this, go ahead and, uh, execute this query. 04:23.520 --> 04:24.360 Let's check it out. 04:24.360 --> 04:30.660 So I've inserted it and then I can go ahead and uh select all. 04:33.690 --> 04:35.910 Select all from. 04:43.050 --> 04:49.530 So go ahead and select all from students and put a semicolon at the end. 04:49.530 --> 04:51.630 And let's go ahead and run this and check it out. 04:51.630 --> 04:54.540 So now we have added this as a last one. 04:54.540 --> 04:59.460 And uh over here you can see we now have 1000 rows. 04:59.460 --> 05:08.800 And uh the stress ID is not One for Marco and Love, and we just have one of each right in here. 05:08.800 --> 05:12.550 So it is no longer duplicates because the primary key is back. 05:12.580 --> 05:13.420 That is it. 05:13.420 --> 05:21.400 So we have seen that we can be able to remove, and it can also add the primary key back to any of that 05:21.400 --> 05:22.060 column. 05:22.240 --> 05:28.360 Now the students or the first name, the last name, the email, the gender, the row, date or column. 05:28.360 --> 05:31.300 So you choose one of these and add your primary key to it. 05:31.300 --> 05:34.780 So your primary key, your primary key is going to always be your neck. 05:34.780 --> 05:40.330 So you add that to either one of them, either the student's ID, the first name, last name, or the 05:40.330 --> 05:43.750 email address, or the gender, or the date or the country. 05:43.750 --> 05:46.810 So you choose one of them and add your primary key to that. 05:46.810 --> 05:48.310 So that is it for now. 05:48.310 --> 05:51.490 And if you have any questions, use the question and answer section. 05:51.490 --> 05:54.190 And I'm going to get back to you as soon as possible. 05:54.220 --> 05:55.180 Thank you so much. 05:55.180 --> 05:58.390 And I'm going to see you in the next video lecture.