1
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So next step, we're moving on to the next subset of logical operators.

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There's a group that fits together nicely, which you're probably familiar with just from middle school

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or early school years.

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And those are greater than greater than an equal to or greater than or equal to less than and less than

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or equal to.

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So for operators, very similar and pretty useful.

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So this is the greater than operator in my SQL.

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It's pretty standard.

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The what is called the alligator bracket.

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00:00:30,570 --> 00:00:32,310
I don't know what to call this, honestly.

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I just call it the greater than bracket.

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It's pretty universal across programming, and it allows us to do things like select all the books released

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after a certain year.

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So select all books where released year is greater than the year 2000.

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And typically we're working with numbers.

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I'll talk about strings in a little bit, but typically we're working with numbers.

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So an example, earlier today I was looking on Airbnb to book an Airbnb and they have a filter that

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allows you to set a minimum price or a maximum price.

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So if I wanted to, I could have gone in and said, I only want to book Airbnbs that have a price greater

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than $50 a night or something to filter out the $20 a night couches and some person's living room.

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So that's powered behind the scenes, most likely by a greater than sign.

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So now let's give it a shot on our own.

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If we hop over here, let's start by just selecting all titles and released here from books, and let's

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just order by release.

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We're just ordering it.

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We'll let us see.

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When we remove things, it will make it clearer rather than having them just be jumbled.

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So we've got 1945 up to 2017.

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Now, if I want to go ahead and do what I showed you, which is select all the books released in the

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2000 or after the year 2000.

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All I need to do is add in where released year is greater than 2000 just like that.

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And if we look, we lost everything.

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From here on back.

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So from Cannery Row to The Amazing Adventures of Kavalier and Clay.

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Important to note that 2000 is not included, which we'll get to in just a moment, but everything greater

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than 2000 is.

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So that gives us all of hoops, gives us all of these books from American Gods down to Lincoln in the

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Bardo.

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As you can see.

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Here we go.

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So that brings us to greater than or equal to, which works exactly the same way, except you add in

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this equal sign afterwards, which makes it rather than greater than it makes it greater than or equal

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to, which means that it's inclusive.

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So if I just change that and do where released here rather than greater than, it's greater than or

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equal to 2000.

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Now it includes the year 2000.

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Let's do one more quick example.

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Let's do a select title and stock quantity from books.

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And let's say that we're going to do a sale because we have some excess stock in some of our books.

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Any book that we have more than 100, including 100, let's say.

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So 100 or more copies in stock.

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We want to select and we're going to discount them.

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So how do we select those?

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Well, it's pretty straightforward.

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We're just going to select title and stock quantity from books where stock quantity is greater than

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or equal to 100.

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And there we go.

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These are the books that we're going to discount.

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All right.

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So there's one other small tangent I want to talk about.

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It's a bit of a diversion away from the tables and books that we've been working with.

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This has nothing to do with any particular data.

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But if you try running something like this, select 99 greater than one.

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What do you expect?

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Well, go ahead and try it if you'd like.

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00:04:08,480 --> 00:04:10,220
I'll go and type it over here.

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Select 99 greater than one.

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00:04:13,940 --> 00:04:17,750
If we hit enter, we get the number one back.

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00:04:17,990 --> 00:04:23,030
All right, so if you're familiar with other programming languages, you've probably come across Boolean

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values.

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True or false values.

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And that's what MySQL is replicating here.

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So the way that it works in Boolean logic is it actually works with the numbers, zeros and one.

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So we know that 99 is greater than one.

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That's true.

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00:04:40,450 --> 00:04:44,310
And so we get one, which is equivalent to true.

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Basically, this evaluates to one which you can think of as evaluating to true.

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00:04:48,330 --> 00:04:51,390
So if if that's confusing you, let's try something.

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00:04:51,780 --> 00:04:59,280
Let's change 99 greater than one to is 99 greater than five, six, seven.

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I just lost it.

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Here we go.

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00:05:01,560 --> 00:05:03,060
We know that that's false.

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And you can see we get zero.

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00:05:06,720 --> 00:05:09,120
So the reason that I'm showing this to you is there's two reasons.

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00:05:09,120 --> 00:05:13,620
One is that it will help us going forward with some of the other things I'm going to show you.

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00:05:13,710 --> 00:05:18,990
When we can start changing things together, you'll be able to evaluate them and kind of do some exercises

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00:05:18,990 --> 00:05:20,070
on your own first.

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00:05:20,640 --> 00:05:25,620
But the other thing and the more important reason is that this is what's happening behind the scenes.

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00:05:25,620 --> 00:05:31,540
When we have something like this right here where stock quantity is greater than or equal to 100.

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You can almost think of it as MySQL, going through every stock quantity and plugging it in here and

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00:05:38,280 --> 00:05:42,350
trying it's 100 greater than or equal to 101.

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00:05:42,360 --> 00:05:43,050
Yes.

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00:05:43,410 --> 00:05:47,850
So keep that one is 23 greater than or equal to 100 zero.

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00:05:47,850 --> 00:05:48,800
No, false.

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00:05:48,810 --> 00:05:52,830
So get rid of that one and it does that going down the line.

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00:05:53,130 --> 00:05:58,530
That's kind of the humanized version, if you will, but it's evaluating to these numbers.

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00:05:58,530 --> 00:06:03,720
But those numbers are just bits and memory, but the concept is the same.

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00:06:04,200 --> 00:06:08,870
So if you'd like, let's wrap this up with just a really simple exercise.

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00:06:08,880 --> 00:06:12,630
I'm going to type up a few things, and I'd like for you to evaluate them yourselves.

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00:06:14,810 --> 00:06:15,070
Okay.

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00:06:15,170 --> 00:06:21,710
So I typed up a couple of examples here, and I'd like for you to just either mentally try these or

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00:06:21,710 --> 00:06:23,030
actually try them yourselves.

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00:06:23,030 --> 00:06:26,810
And remember, you'll need to actually run, select and you'll need a semicolon.

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00:06:26,810 --> 00:06:29,720
But what's the result that you expect?

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00:06:30,050 --> 00:06:36,260
And there are a couple of straightforward ones, and then I threw in two string ones at the end, basically

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00:06:36,260 --> 00:06:37,400
to give myself a talking point.

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00:06:37,400 --> 00:06:41,540
At the end, I want to talk about why this happens and if you should care.

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00:06:41,810 --> 00:06:43,040
So go ahead.

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00:06:43,040 --> 00:06:45,260
I'll throw up a thing on the screen that says you should do it.

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00:06:45,770 --> 00:06:47,840
And then in like 2 seconds, I'll be back.

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00:06:49,570 --> 00:06:50,710
All right, I'm back.

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00:06:51,040 --> 00:06:54,730
So first one, 100 greater than five.

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00:06:54,760 --> 00:06:55,600
Is that true?

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00:06:55,720 --> 00:06:58,300
Well, yes, I believe that to be true.

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00:06:58,330 --> 00:07:01,770
Just to double check, it gives us one.

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00:07:01,780 --> 00:07:02,920
That means we're in the clear.

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00:07:03,640 --> 00:07:04,950
-15.

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00:07:04,960 --> 00:07:06,050
Greater than 15.

119
00:07:06,070 --> 00:07:07,150
Is that true?

120
00:07:07,240 --> 00:07:10,810
Well, no, I don't think so.

121
00:07:11,590 --> 00:07:12,610
And we get zero.

122
00:07:12,910 --> 00:07:13,510
All right.

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00:07:13,990 --> 00:07:16,300
Nine greater than negative ten.

124
00:07:17,590 --> 00:07:19,290
That seems like it should be true.

125
00:07:19,300 --> 00:07:20,260
And it is.

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00:07:20,800 --> 00:07:23,320
What about one greater than one?

127
00:07:25,400 --> 00:07:28,310
Well, I don't think one is greater than one, so it's false.

128
00:07:28,340 --> 00:07:31,700
However, if there was the equal sign, of course it would be true.

129
00:07:32,180 --> 00:07:32,750
All right.

130
00:07:33,020 --> 00:07:34,340
Now, these two.

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00:07:35,160 --> 00:07:42,600
String comparisons with greater than less than is notorious in all languages, for one being annoying

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00:07:42,600 --> 00:07:46,170
and confusing, and two differing radically between languages.

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00:07:46,170 --> 00:07:51,870
So the advice that I would give to anyone is to just avoid ever having to do anything like this.

134
00:07:51,870 --> 00:07:55,190
There are ways around it, but I just wanted to show you what happens.

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00:07:55,200 --> 00:08:01,650
So what do you think is the lowercase A It comes before B, so is it greater than or less than B?

136
00:08:02,430 --> 00:08:04,410
And in some languages it is greater than.

137
00:08:04,410 --> 00:08:09,030
In others it's less than in my SQL case, my SQL.

138
00:08:10,080 --> 00:08:16,410
If we hit enter, we can see that A is not greater than B, meaning that it's less than B.

139
00:08:17,370 --> 00:08:22,380
Although technically that statement is logically wrong because it could be equal to B.

140
00:08:22,380 --> 00:08:26,280
But as you can see, if I add that equal sign, it's still false.

141
00:08:26,430 --> 00:08:29,490
So we know definitely A is less than B.

142
00:08:30,480 --> 00:08:37,409
So that brings us to our last one, which is a bit tricky, uppercase a greater than lowercase a and

143
00:08:37,409 --> 00:08:38,429
if we run that.

144
00:08:40,600 --> 00:08:42,870
With the semicolon, you'll see that it's false.

145
00:08:42,880 --> 00:08:46,060
So uppercase A is not greater than lowercase a.

146
00:08:46,120 --> 00:08:49,930
So then does that mean that it's lower?

147
00:08:50,680 --> 00:08:53,890
Does uppercase a come before lowercase a?

148
00:08:54,010 --> 00:09:00,160
And the answer is actually, if we change this just slightly to be greater than or equal to, you'll

149
00:09:00,160 --> 00:09:00,340
see.

150
00:09:00,340 --> 00:09:01,360
Now it's true.

151
00:09:01,540 --> 00:09:09,580
So that tells us uppercase a is equivalent to lowercase A in my school's eyes and we've seen that before.

152
00:09:09,580 --> 00:09:13,630
When we do something like, well, let me just type it again.

153
00:09:13,630 --> 00:09:23,590
Select author l name where author l name equals.

154
00:09:24,550 --> 00:09:31,960
If we do eggers like this and of course I add in the all important table name from books.

155
00:09:34,090 --> 00:09:41,890
So if I do this and let's also do title just to make it easier to see what's going on, it matches just

156
00:09:41,890 --> 00:09:42,520
fine.

157
00:09:43,120 --> 00:09:46,780
But I can also do this with lowercase e and it works just the same.

158
00:09:46,780 --> 00:09:53,470
Or I can do Edgar's like that with two uppercase G's, so the way that string comparisons work in my

159
00:09:53,500 --> 00:09:54,850
SQL is quite odd.

160
00:09:54,970 --> 00:09:59,200
And if you're familiar with other languages, it's very different from pretty much every language I've

161
00:09:59,200 --> 00:09:59,860
worked with.

162
00:10:00,280 --> 00:10:03,700
So just something worth noting that case doesn't actually matter.