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that we can't delete Unidentified artist, because it's
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referenced in the created table.
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What we should maybe first do is delete this row delete their affiliation
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with their work, and then delete the artist so we don't
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run into this FOREIGN KEY constraint.
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So let's try this in our SQLite environment.
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Come back to my computer.
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And again, our plan was to first delete the artists affiliation with their work
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from the created table.
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So let me show you first the created table.
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I'll say SELECT [? star ?] from "created,"
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and see how it's exactly like the table we just visualized.
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Now, let me try delete this artist affiliation with their work.
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I'm not deleting the artist.
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I'm deleting their affiliation with their authorship,
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their [? artist ?] [? ship, ?] whatever you want to call it for their work.
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Now, I'll say DELETE FROM--
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let's say, DELETE FROM "artists" WHERE the "artist_id" is equal to
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or equals 3.
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Well, I could do this.
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But there's probably a better way, like I know the id, and that's fine.
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But we could also use, as we saw a little bit ago,
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which were [? subqueries, ?] a way to write a query that
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returns me the result. And that result gets included in another query
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altogether.
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So let's try that instead.
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Let's say I don't know the artist_id.
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What I could do is make a [? subquery. ?]
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I could say inside of this, let me select the "id" FROM the "artists"
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table WHERE, in this case, the "name" equals "Unidentified artist," and then,
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let me close out this query, hit a semicolon.
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And I already see a typo in this, but I'm just going to try it anyway.
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I will go ahead, and hit Enter.
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And let's see if I type SELECT [? star ?] FROM "artists," Enter,
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I still see Unidentified artist.
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And I think my typo here was as follows.
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If I up my query using the up arrow on my keyboard,
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I see DELETE from "artists," where the "artist_id" equals some value here.
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But do I want to delete from artists?
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I don't.
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I actually can't delete from artists.
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What I should do instead is delete from the created table.
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So let's try this.
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I'll say DELETE FROM "created," making sure I only
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have double quotes around created, then I'll
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say WHERE the artist_id equals, let's say, either 3--
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but it could also be the result of this [? subquery. ?]
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I'll say 1, 2, 3, 4, and then SELECT the "id"
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FROM the "artist" table WHERE the "name" equals "Unidentified artist."
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Then I'll close this [? subquery, ?] hitting semicolon, hit Enter.
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And now, if I say SELECT [? star ?] FROM "created" semicolon,
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I should see that this artist's affiliation with their work
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no longer exists.
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And because it no longer exists.
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I can now delete them from the artists table.
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I don't have this FOREIGN KEY artist_id referencing
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the primary key of this artist.
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So let's now try that.
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I could say SELECT [? star ?] FROM "artists,"
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I see that Unidentified artist is still in here.
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But let's delete them now.
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I'll say delete from, let's say, "artists" WHERE
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the "name" equals "Unidentified artist," closing my quotes, semicolon, hit
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Enter.
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And now if I Select [? star ?] FROM "artists" semicolon,
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I should see they're no longer in this table to our earlier example.
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This becomes a 2-step process.
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First delete their affiliation, then delete their name.
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OK, So let's try this yet again, but now using some additional tools
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that we have at our disposal.
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So let's look back at this FOREIGN KEY constraint that existed in this table.
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If you remember, it looked a bit like this.
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In my created table, I had this line.
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FOREIGN KEY, artist_id, REFERENCES the "id" column in "artists."
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Well, if that is the case, I can't delete the artist with the id
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referenced by this [? foreign ?] [? key. ?] But it turns out that I
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could specify some alternative action that happens when I try to delete
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the id that is referenced by this [? foreign ?] [? key. ?] I can specify
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that using a keyword called ON DELETE.
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So after FOREIGN KEY REFERENCES [? "artist id," ?] I could say
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afterwards ON DELETE, and then specify some action I want to actually happen
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when I tried to delete the primary key referenced by this [? foreign ?]
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[? key. ?]
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One thing I could use would be RESTRICT, which
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is kind of like what we saw before.
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If I try to delete a primary key is [? referenced ?] by this [? foreign ?]
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[? key, ?] I will not be allowed to do it.
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That action is restricted.
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I could also decide to take NO ACTION.
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In this case, I could delete the primary key [? referenced ?] by this
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[? foreign ?] [? key, ?] and nothing would happen.
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I would actually be allowed to do that, which may be unwise in some cases,
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but I could give myself that power.
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I could also decide to SET NULL.
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That is if I delete the primary key that is [? referenced ?] by this
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[? foreign ?] [? key, ?] what I'll do is set the [? foreign ?] [? key ?] to be
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NULL, meaning that value no longer exists.
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I can alternatively [? set ?] it to a [? default ?] value for that column.
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Or perhaps, most compellingly, I could try to CASCADE the deletion.
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Where CASCADE means if I delete the artist, for instance,
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