00:00What's going on, everybody? Welcome back to another video. Today, we are continuing our
00:04PostgreSQL series. This is the very first lesson where we actually start querying data,
00:08and we're starting with the select and the from statement. Now, these are some of the
00:12most important ones because they select the data and they choose where that data is coming from.
00:17These are very important concepts. They're going to be in every single SQL query you write,
00:22basically ever, unless you're doing something like create table. But if you're querying data,
00:26you're going to have a select and from. That's just a fact. So understanding these concepts will
00:30last you a lifetime. So let's go ahead and take a look at how we can query this data.
00:35Now, we already created our tables in the last lesson. If you haven't done that already,
00:40I will leave a link to this right here. This is just our script for creating our tables
00:44and inserting our data. That's it. I will leave a link to this down below where you can download it
00:49from GitHub. Super easy. You just run it and then you're good to go. Now, let's actually get into
00:54the lesson. So what we need to do first is we need to write out select. And if you read
01:00that
01:01and you said something is wrong, I'm really proud of you. You're probably already ahead of the game
01:05and you know what's wrong here. Typically, when we have these commands in SQL, we write them in
01:10all caps. Now, it doesn't have to be. The query will technically run perfectly fine if it's all in
01:17lowercase. But it's kind of an unwritten rule of formatting your queries to have the commands in
01:22all caps. Now, I'm going to be doing that for 99% of the queries in this lesson. You don't
01:28have to.
01:28You can be a renegade and you can just do what you want. But that's what we're going to do.
01:33Now, let's go ahead and we're going to do select star. Now, what star means is it means everything.
01:39This means that if we select our character info or our planets or our ships, it's going to give us
01:44all the columns and all the rows of data. Now, this can be a little bit trickier as you start
01:49working with huge amounts of data because just selecting everything from a table could take
01:53minutes or, you know, an hour. If you have a ginormous data set, that'll just take forever to
01:59return. But we're going to select everything. Then we're going to go to the next row. And this is
02:03typically how you format a SQL query. Then we're going to write our next one, which is from. So we're
02:08selecting everything. But where are we actually selecting it from? We have to specify.
02:13So let's start with our character info table. So we're going to say character underscore info.
02:20And that's it. Select everything from character info. Let's go ahead and execute this script.
02:26And just like that, it says it ran successfully and it's returned all of our columns and all of
02:32our rows of data. Really briefly, let's just look at these columns. We have character ID, character name,
02:37species, planet ID, ship ID, estimated net worth, if they have both arms and their birth
02:44date. So this is our data, right? We have these columns. And in each column, we have different
02:50rows. That's each of these one, two, three, four, all the way down to 12. Now, when we're selecting
02:54from something, we can specify what we want to select. Now, there are a lot of different things
03:00included in the series. But even just in the select statement, there's a lot of things that
03:04we can do. For example, if we don't want to select everything, we don't want all of our columns,
03:09we can get rid of that star and we can specify the columns that we do want. For example, let's
03:15pull
03:16up the character underscore name and we can actually include multiple column names. All we have to do
03:21is separate it by a comma. So we're going to do character name and then we'll do, it's going to
03:26take
03:26a while. Estimated net worth. Let's go ahead and run this. And this looks perfect. So now we have
03:36specified different columns that we want. And in our output, that's all we have. Now let's come
03:42right down here. We're going to go below it. Because when I'm writing SQL queries, I typically
03:46don't just have one in here. I have multiple. I have three, four, five, six queries. And as it gets
03:52more advanced, they're kind of building on each other with temporary tables and CTEs and all these
03:57different things. It gets very complex. And so I typically don't just have one query. I have
04:02multiple. So let's come down here. Let's select everything from a different table. So we're going
04:06to do our ships table. So I'm going to do select everything from ships. Now this looks great, right?
04:15Let's go ahead and run this. Uh-oh, there is an error. And the error is not obvious at first.
04:20In fact,
04:21when I was first learning SQL many years ago, I was really confused about this. In a SQL editor,
04:27you can't have two queries run at the same time unless you have them separated. And you do that
04:32using a semicolon. So now that it has a semicolon between this code and this code, I'm calling it
04:38code, but it's, you know, just a query. Let's go ahead and execute this. And now we get our output.
04:44So it ran successfully. But you'll notice we only have one output down here. And that's fine.
04:50If we want to specify just this one, we can highlight over it. And then we can run it.
04:57And it's going to run this query instead. If we run the entire thing, it's just going to run
05:03the last query. So right here. Now typically at the end of all my queries, I put a semicolon just
05:09by default, just in case I do want to write something beneath it. But that's just extra information.
05:15I'm throwing stuff at you. But just extra information in case you want it. Let's bring
05:20this down a little bit. Something I do in the select statement a lot is I create new columns.
05:27And this is very, very common. Let's copy this. And I'm going to bring this right down here. And I'm
05:33just going to say select everything. And I only want to run this one. So let's go ahead and do
05:38that.
05:39But let's say I want to take their estimated net worth. And I just want to multiply it by
05:44something. That would be something that I can do in the select statement. So let's take
05:48estimated. And actually, let me copy this because I don't trust my spelling skills here. But I'm
05:55going to do a comma. And now we're going to do something. I'm going to take the estimated
05:59net worth. I'm going to do a star two. That's going to take the estimated net worth. It's going
06:04to multiply it times two. Now let's go ahead and run this. And right here, you'll see there's
06:11150,000. Now it's 300,000. You're also going to notice that there is no column name. It's
06:18question mark, column, question mark. And that is not helpful. So what we can actually do in the
06:23select column is use an alias. Now an alias just renames a column to something else. So what we're
06:31going to do is we're going to say as, and we can say double the worth. And this is going
06:39to rename
06:39this column as double the worth. Let's go ahead and run this. And there we go. So we rename that
06:46column to double worth. And now we have estimated net worth and double their worth. So we're able to
06:51perform calculations in the select statement as well. Now we don't have to do that with just this
06:57column because it didn't have a column name. We could do that with anything. So if we
07:01ran this query up here, we could rename this one and we could say as name. And if we run
07:08this one
07:08again, you'll see right down here. Now it says name. Now this gets really helpful the more advanced
07:14we get. So when we get to things like subqueries, CTE, window function, these are things where aliasing,
07:20not just in the select statement, but also in the from statement, aliasing becomes a lot more
07:25important. So we'll get to that in a future lesson to dive more into the advanced kind of pieces of
07:30aliasing, but we won't in this lesson. By now, you should feel really comfortable using select and
07:36from. Go ahead and try it out. Mess around with it. Select different tables, select different columns.
07:41And in the next lesson, we're going to start looking at the where statement where we can start
07:45filtering our data. If you learned anything in this lesson, be sure to like and subscribe,
07:49and I will see you in the next video.
Comments