WEBVTT 00:07.820 --> 00:08.540 All right. 00:08.540 --> 00:13.070 So let's go ahead and look at primary keys in PostgreSQL. 00:13.310 --> 00:18.920 So in PostgreSQL we have this uh data set we inserted. 00:18.920 --> 00:25.940 And if we go over and check out the students let's go ahead and say students and hit enter. 00:27.200 --> 00:29.510 We have these students PK. 00:29.510 --> 00:31.400 And that is the primary key. 00:31.430 --> 00:36.350 So we can see we have this primary key and that is the students ID. 00:36.620 --> 00:43.970 And over here you can see the stress ID pk the bigint is a primary key. 00:43.970 --> 00:48.800 And uh we want to learn more about this primary key. 00:49.010 --> 00:59.120 Now this primary key helps us to be able to restrict to datas with same information. 00:59.120 --> 01:04.980 So nobody in this place, we have the same primary key of like one and N1. 01:05.220 --> 01:07.350 Let me go ahead and show this. 01:07.380 --> 01:12.540 This is what we have in the previous lecture and this is what we inserted. 01:12.540 --> 01:15.360 And we have this guy right in here. 01:15.360 --> 01:17.520 And this is a very fast one. 01:17.520 --> 01:23.730 And it has the name Mark on and the ID is one. 01:23.760 --> 01:24.990 Let's go ahead and check it out. 01:24.990 --> 01:27.570 So the ID of this guy is one. 01:27.570 --> 01:35.580 Now you can see it has a primary key of one uh ID one that is stress ID and the stress ID two. 01:35.610 --> 01:39.780 Now we can have the same person having the same primary key. 01:39.810 --> 01:41.550 Like this guy here. 01:41.550 --> 01:43.500 It is not possible at all. 01:43.590 --> 01:47.070 If we go ahead and try that, we're going to run into an error. 01:47.400 --> 01:51.690 Let's go ahead and open up the Visual Studio. 01:51.720 --> 01:56.970 And I'm going to say I want to insert into this. 01:57.000 --> 02:02.730 Let me go ahead and say insert into students and I'm going to add a student. 02:05.190 --> 02:08.130 That is a stress underscore ID. 02:08.740 --> 02:17.020 and now if I go over here and add this ID one here and try to copy this, let me go ahead and copy this 02:17.020 --> 02:18.910 and insert that. 02:18.940 --> 02:21.640 I want to insert this. 02:21.670 --> 02:23.530 And now I copied this. 02:23.530 --> 02:25.750 And I'm going to minimize this right in here. 02:25.750 --> 02:33.460 If I go over to this place and I try to insert that into the students table, I'm going to get an error. 02:33.460 --> 02:37.360 So go ahead and clear this and I'm going to press what I just copied right in here. 02:37.360 --> 02:41.260 And then go ahead and reduce this value so I can be able to see it. 02:41.860 --> 02:42.220 All right. 02:42.220 --> 02:44.080 So insert into students. 02:44.080 --> 02:52.690 And now with our students ID then first name last name email gender error date country and values is 02:52.690 --> 02:53.680 equal to one. 02:53.680 --> 02:55.390 Now let's go ahead and execute this query. 02:55.390 --> 02:56.260 Let's check it out. 02:56.290 --> 02:58.240 Now you can see you have an error. 02:58.240 --> 03:03.910 And what this error said is duplicate key value varies unique constraint. 03:03.940 --> 03:06.880 Students peak t. 03:07.060 --> 03:09.940 So that is the student ID. 03:09.970 --> 03:15.110 It's also said here that our a stress ID equal to one already exists. 03:15.140 --> 03:17.150 That's duplicate key value. 03:17.180 --> 03:21.530 Whereas the unique constituents which is the primary key. 03:21.710 --> 03:27.920 Now you can see that we have a very big problem because I'm not a not a problem at all. 03:27.920 --> 03:34.910 So this helps us to actually make sure I would not have these two, uh data bit inserted. 03:34.910 --> 03:42.740 And in that case it's going to give us a very big issue, because in a case where two persons have the 03:42.740 --> 03:46.250 same ID, we are going to always run into problem. 03:46.250 --> 03:54.740 So if you want to actually do that, all you need to do is you have to go ahead and, uh, drop the 03:54.740 --> 03:57.050 primary key if you want to insert this. 03:57.050 --> 04:04.730 And if I want to drop the primary key or I need to do is to go ahead and drop this constraint, call 04:04.760 --> 04:07.310 the answer key. 04:07.610 --> 04:08.900 Go ahead I see it. 04:09.080 --> 04:12.620 So I'm going to start by deleting everything I have right in here. 04:12.620 --> 04:16.630 And then I'll go ahead and use a keyword called quarter. 04:16.630 --> 04:20.560 And then I'm going to alter the turbo and the turbo. 04:20.590 --> 04:25.390 I want to alter is this to stable students. 04:25.570 --> 04:30.520 And then I'll go ahead and drop using drop keyword. 04:30.520 --> 04:32.950 And what I'm going to drop is this constraint. 04:32.980 --> 04:33.400 All right. 04:33.430 --> 04:35.500 Because you can see unique constraint. 04:35.530 --> 04:38.980 So why I say constraints. 04:41.170 --> 04:45.070 And now what is the name of the constraint that is to name the key. 04:45.220 --> 04:56.590 So I'll go ahead and say the students uh underscore p key and put a semicolon at the end. 04:57.040 --> 05:01.360 Now if I have this I'll go ahead and this to this and check it out. 05:01.390 --> 05:03.850 Our table query returned successfully. 05:03.850 --> 05:10.540 And you can see that now if I go ahead and delete everything I have here and, uh, paste back what 05:10.540 --> 05:17.680 I just copied from Visual Studio and execute this query, we can see insights are zero. 05:17.710 --> 05:19.990 One means return successfully. 05:20.030 --> 05:28.640 And if I should go ahead and delete everything here and I'm going to say select all from students, 05:28.640 --> 05:31.910 I put a semicolon at the end and the score had I checked out. 05:31.910 --> 05:37.400 And now if you go down let's go ahead and move down. 05:37.430 --> 05:42.800 Down here you can see we have our this has moved over to 1001. 05:42.800 --> 05:46.430 And last we can see Mark con is equal to this. 05:46.550 --> 05:53.870 And if we go ahead and select that from here I can go ahead and say select from students. 05:53.870 --> 05:59.480 Where I'm going to say we are students. 05:59.510 --> 06:03.380 Underscore ID is equal to one. 06:03.380 --> 06:08.300 And if I should go ahead and run this, we can see we have Mark home. 06:08.540 --> 06:11.090 And it appears twice. 06:11.900 --> 06:17.390 So but this is not really very nice because you're not supposed to have this right. 06:17.390 --> 06:18.890 So I hope that is very cool. 06:18.890 --> 06:25.290 So this is the importance of the ID that is the primary key. 06:25.320 --> 06:25.980 This is important. 06:26.010 --> 06:29.910 The primary key in query or in PostgreSQL. 06:29.940 --> 06:36.810 It helps you to avoid having two data and conflicting data, because there is no how you can know who 06:36.810 --> 06:37.710 is Marco. 06:37.740 --> 06:38.610 Right in here. 06:38.610 --> 06:41.520 And who has this or who is this? 06:41.520 --> 06:47.490 Because everything is just the same and you don't want to run into that problem. 06:48.210 --> 06:54.090 So we have the first name, the last name, the same email address, same gender, uh, enrolled date 06:54.090 --> 06:55.680 and from the same country. 06:55.710 --> 06:58.020 And now you have a very big problem. 06:58.020 --> 07:05.310 And if you have different stress ID, you can actually use that to separate them and know who is who. 07:05.310 --> 07:06.930 And that would have been better. 07:07.200 --> 07:09.480 So let's go ahead and put this done. 07:09.480 --> 07:10.230 Practice with it. 07:10.230 --> 07:14.910 And in the next video lecture we'll go ahead and put this back again and have a primary key right in 07:14.910 --> 07:18.450 here because that is very, very, very important. 07:18.480 --> 07:19.020 Thank you. 07:19.020 --> 07:21.780 And I'm going to see you in the next video lecture.