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The next thing we'll see is how we can modify existing columns, not their name, but modify the actual

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column definition.

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So in this example, I'm altering the table suppliers to modify the biz name column so that it is a

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var car 100, whatever it was before it is now a var car 100.

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Now we have to be somewhat careful with this, of course, because if you had a numeric column that

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you were turning into text or text, you're turning into numeric or a date column, you're suddenly

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turning into an int that could cause a lot of issues.

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You want to you want to be very conscious of that.

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But I'm just going to show you a simple example.

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Let's say that I realized I wanted something to be not null and it was currently knowable and I want

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to make it a var car with a larger size.

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So we've got I don't know, let's go back to companies.

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We have var car 255 for name.

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Let's actually shrink that down.

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Sure.

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So I renamed that column to company name, if you remember.

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Here, let's do describe companies.

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Here we are.

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We see that company name is var two, five, five.

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So let's say maybe I want to add a default value.

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And I also want to make it a var card 100.

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We're enforcing a shorter limit for our var cards.

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This is stupid, but let's just do it.

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So I'll do an alter table companies if that's still the name, of course.

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And then modify.

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And what am I trying to modify?

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The company name column.

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Whoops.

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This way.

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Company name.

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And now I can say I want it to be a var char.

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Uh, 100 and then give it a default value of a name.

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Unknown Something like that.

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If you put a company in here, we don't know the name, then its default will be unknown.

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So right now it's var 255.

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Oh no.

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I have these quotes there that might cause me trouble.

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Let's try that again.

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All right, I run it.

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Let's describe.

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Where are you companies?

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It's still called company name, but now var 100 is the type.

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And we see that default is set to unknown.

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And if I were just to quickly insert into companies, we have company name and address values.

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Let's insert no company name.

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So I'm going to leave that off.

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That was the whole point I wanted to show.

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So let's only insert the address and address will be two five, five, four Rose Lane.

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And if I now select star from my companies, we see the default for company name kicked in, which is

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unknown, and that's what we get instead of null.

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All right.

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So that's how you can modify a column by changing its type.

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There's also a second option.

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If you wanted to rename a column and change its definition, you can use change.

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So I use this less often because a lot of the time I might just want to modify an existing column,

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not rename it.

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But if you use change, you have to say the current column name, then the new column name and then

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the new column definition.

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So this is saying take the supplier's table, change the business column, rename it to biz name, and

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set the definition to be a var of 50.

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So I don't think I need to show an example of that.

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It's the same concept, right?

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We just have to say old name, new name definition.

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Whereas when we modify, we don't have the opportunity to change the name of a column.

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But it's simpler.

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We only say, Here's the current name and the new definition for that current named column OC.