WEBVTT 00:07.640 --> 00:09.740 Okay, I will call you back again. 00:09.770 --> 00:14.600 So in this PostgreSQL lecture we are going to look at left join. 00:14.600 --> 00:20.000 So in the previous lecture we looked at join and we can see how we join these two tables. 00:20.000 --> 00:21.770 But there is one thing here. 00:21.770 --> 00:29.870 If you look at the table with join we have another strange table about four of these rows. 00:29.870 --> 00:38.000 And when we join these we have only three rows because we joined only students that have phones assigned 00:38.030 --> 00:38.660 to them. 00:38.660 --> 00:46.130 Now as a data analyst you may be asked, oh, and need you to present to me the data set of every student 00:46.130 --> 00:50.000 in this school who have bought phones and who doesn't have phones. 00:50.000 --> 00:53.990 And you'll be like, how can I be able to achieve this? 00:54.110 --> 00:57.920 So that is where the left join comes into play. 00:57.920 --> 01:05.730 So the join method, we actually or the join keyword, we only give you people who assigned phone to 01:05.760 --> 01:09.030 them or who assigned anything to them. 01:09.030 --> 01:14.940 But the left join will give you what students who have phone assigned to them, and students who do 01:14.940 --> 01:16.680 not have phone assigned to them. 01:16.680 --> 01:18.810 And now let's go ahead and do that. 01:18.810 --> 01:22.110 So this is just the same thing we would have just done. 01:22.110 --> 01:25.860 And I'm going to do it instead of me going over to do this. 01:25.890 --> 01:32.160 Let's go ahead and simply select whatever we have here so that you will know that all these are still 01:32.160 --> 01:33.720 the set already. 01:33.750 --> 01:36.930 And I'm going to select all from here. 01:36.930 --> 01:39.570 And I'm going to press that just down here. 01:39.570 --> 01:42.960 And I'm not going to put a semicolon at the end. 01:42.990 --> 01:44.400 Go ahead and hit enter. 01:44.430 --> 01:50.280 Now if I shoot one here and copy this join and copy this. 01:50.310 --> 01:53.970 If I press that day I'm going to replicate exactly this. 01:54.000 --> 01:58.890 But now I'll go ahead and add left and then press what I have. 01:58.890 --> 02:07.740 So I have left join phone on on a new table created student dot phone underscore ID equal to funded 02:07.740 --> 02:07.780 80. 02:07.780 --> 02:16.210 And if I hit this now, you can see that I have this new tool created and I have the razor line. 02:16.240 --> 02:17.140 Voila! 02:17.170 --> 02:21.400 Assigned under this, but without a phone. 02:22.060 --> 02:27.670 So you can see that we are able to get both students who we are, who have phone assigned to them, 02:27.670 --> 02:31.600 and students who don't know how phone assigned to them in left join. 02:31.600 --> 02:34.840 So the left join helps you to add everything together. 02:34.870 --> 02:40.360 But when you use the join keyword alone, you just get people have this assigned to them alone. 02:40.960 --> 02:45.970 So this is applicable when I go ahead to select a specified columns. 02:45.970 --> 02:52.780 If I go ahead and copy this and come over here and I go ahead and press this and hit enter a warhead 02:52.780 --> 02:55.660 and say from student I'm going to copy this. 02:55.720 --> 02:57.880 Remember that this is what we did in previous lecture. 02:57.880 --> 03:04.690 So I'm trying to replicate that so you can be able to follow on without getting uh distracted or confused. 03:04.690 --> 03:06.130 So I'll go ahead and copy this. 03:06.130 --> 03:10.690 And then over here I'll just go ahead and add the left and press this. 03:10.690 --> 03:15.040 Now hit enter and you can see that I have four rows. 03:15.040 --> 03:18.280 And in the previous lecture we have three rows. 03:18.310 --> 03:27.790 Now you can see guru has Motorola, Tokubei has image, George has and Song Wang Rosalind has been assigned 03:27.820 --> 03:28.810 to her. 03:29.350 --> 03:37.960 So that is the difference between, uh, the join method or the join Kuwait and the left join keyword. 03:37.990 --> 03:38.770 Now that is cool. 03:38.770 --> 03:42.580 So what if you are asked to get students who don't have anything assigned to them? 03:42.580 --> 03:43.960 How can you be able to do that? 03:43.960 --> 03:48.040 So that is very simple a while and say select uh. 03:50.530 --> 03:52.600 I want to select all. 03:52.600 --> 04:05.680 Then from the students table the algorithm is where class where uh the font ID because this is the font 04:06.940 --> 04:08.200 ID right. 04:08.200 --> 04:10.780 So we're using the font ID to actually check this. 04:10.780 --> 04:17.600 So we are the font underscore ID Is no. 04:17.630 --> 04:19.490 Put a semicolon at the end and hit enter. 04:19.490 --> 04:23.480 And you can see we have Rosa Len, uh, Mayweather. 04:23.480 --> 04:26.840 And no phone was assigned to her. 04:27.170 --> 04:27.530 All right. 04:27.560 --> 04:34.250 So this is how you can be able to check out the student who has no phone assigned to him or her. 04:34.250 --> 04:36.800 And, uh, you can be able to display that out. 04:36.800 --> 04:40.790 And this helps us to display every student that has phone assigned to him or her. 04:40.790 --> 04:43.250 And that is the power of the left join. 04:43.250 --> 04:48.230 So the right the join actually gives you only people who are all have phone assigned to them. 04:48.230 --> 04:53.900 What's the left join gives you everybody who have puts phone or no phone assigned to him or her, and 04:53.900 --> 04:58.760 you get the data set for your own purpose or whatever you want to do with it. 04:58.760 --> 05:00.140 So that is it for now. 05:00.140 --> 05:03.140 On left, join while I put it down, practice with it. 05:03.140 --> 05:06.620 And if you have any question, what had I use the question and answer section? 05:06.620 --> 05:09.080 And I'm going to get back to you as soon as possible. 05:09.110 --> 05:10.070 Thank you so much. 05:10.070 --> 05:12.890 And I'm going to see you in the next video lecture.