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24.9
It's not in our database.
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2.29
We can actually put together a condition around this idea of null, something
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4.52
not being there.
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1.71
We could use IS NULL to figure out if a value is null.
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3.57
It's not there.
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0.658
It's missing from our database.
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1.292
Or IS IT NULL, meaning that it actually is there.
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4.763
So I'll go back to SQLite and show you what we could
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do with some of these concepts here.
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3.52
Let me go back to my terminal.
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1.43
And let's say I do want to find those translators that
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3.12
don't exist in my database.
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2.08
Well, I could use SELECT, let's say, "title" and "translator" from my
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6.8
"longlist."
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1.05
And I want to make sure that these translators are null--
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4.11
they don't exist.
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1.36
So I'll say WHERE "translator" IS NULL Semicolon.
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5.33
Now, I'll hit Enter.
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1.53
And I should see two books.
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1.438
Titles are The Perfect Nine and the indictment of The Enlightenment
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2.792
of The Greengate Tree.
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0.917
But notice how over here, this value is null--
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3.403
it doesn't exist in my table.
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2.74
I could conversely find those books that do have translators using IS NOT NULL.
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5.27
And I will try this one again.
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2.71
But in this case, I'll say, WHERE "translator" IS NOT NULL Semicolon.
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7.85
And I'll hit Enter.
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1.77
And now, let me just zoom out a little bit.
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2.67
I can see that I have both titles on the left-hand side
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5.13
and translators on the right-hand side.
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2.31
All of these actually exists.
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2.26
These are books that did have translators in this case.
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3.679
So a good way to find data that's missing in your table using
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3.091
NULL or IS NOT NULL.
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2.822
So let's come back over here and figure out what more
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2.208
we can do with some of these queries.
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2.67
We've kind of exhausted our work with some of our conditions,
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4.95
like chaining them together and using NULL and so on.
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2.35
But one more thing we could do is trying to use this idea of matching
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4.73
some kind of pattern in my database.
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2.349
So maybe I'm a book reader.
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3.591
And I want to find a book with the word "love" somewhere in the title.
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3.989
Well, for this, I could use another keyword--
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2.551
this one called LIKE.
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2.25
So LIKE is a good keyword to use when I want to roughly match
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some string in my database.
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2.281
Let's say I want to look at book titles and find
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2.43
if some word exists in that title.
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2.52
I could use LIKE for that.
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2.41
And LIKE becomes powerful when you combine it
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2.36
with these other operators, namely this percent sign and this underscore.
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4.4
The percent sign can match any character around a string I give it.
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4.78
And the underscore can match any single character
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3
that I pass in with my string.
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2.37
It's probably best shown with an example.
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2.47
So let me show you some in my terminal here.
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2.81
I'll walk back.
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1.05
And, again, we'll try to find these books that
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2.07
have "love" somewhere in the title.
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2.85
So I'll say in this case, SELECT, let's say, "title" from "longlist."
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5.97
But I don't want all titles.
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1.68
I only want those that have "love" somewhere in this title.
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4.06
So I'll say WHERE "title" LIKE, let's say, percent love percent Semicolon.
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9.71
Now before I run this, let me explain what this is doing.
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3.99
I have here a SELECT query asking for the "title"
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3.96
column from my "longlist" table.
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3
But I'll only get back those rows where "title" is LIKE percent love percent.
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6.51
But what does that mean?
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1.42
Well, the percent, remember, matches any string of characters.
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3.8
It could match a, b, c, 1, 2, 3.
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2.25
As long as any string of characters comes after and has "love,"
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3.69
I could match that value here.
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3.19
Similarly, the percent sign after says anything
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2.585
that comes after "love," as long as "love" is somewhere in the middle.
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4.585
So anything before, anything after, but so long as "love"
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3.59
is just somewhere in there, I'll get it back.
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2.31
So let me try that running this query then and come back over here.
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3.75
I will hit Enter on my query.
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2.25
And I'll see I get back four books--
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2.52
Love in the Big City, More Than I Love My Life and so on.
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4.06
So notice how if I come back over here that each of these titles
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3.77
has "love" somewhere in it.
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1.83
For this one, I match love up front and then
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3.42
had any string of characters coming after it like this.
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2.8
For this one, I had More Than I Love My Life.
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2.75
I got some string before it.
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1.71
And then afterwards, any string after it, "love" is somewhere in the middle.
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5.19
Let me show you another example too, where
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2.07
we use percent in a different way.
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2.71
Let's say I want to find only those books that
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2.51
have "The" at the very beginning of the title.
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3.45
Let me try this.
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1.09
I'll say a SELECT "title" from "longlist" then WHERE,
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6.47
let's say, the "title" is LIKE the percent Semicolon.
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9.08
Now, I've changed something up.
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1.9
I have not percent in front and behind, but only after the "The."
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5.9
So in this case, I'll get back not anything
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2.91
that has "The" the title wherever, but now
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3
at the very beginning of this string.
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2.94
And I see perhaps a style mistake.
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3.03