Re: Alter table column constraint

On 12/17/2018 02:20 PM, Rich Shepard wrote:
> On Mon, 17 Dec 2018, Melvin Davidson wrote:
>
>> Yes, you must drop then add the revised constraint. However, from your
>> statement above, it sounds to me as if you would be better off using A
>> FOREIGN kEY CONSTRAINT. It makes things a lot simpler.
>
> Melvin,
>
>   I don't follow. Here's the DDL for that column:
>
> industry varchar(24) NOT NULL
>     CONSTRAINT invalid_industry
>     CHECK (industry in ('Agriculture', 'Business, other', 'Chemicals',
>     'Energy', 'Law', 'Manufacturing', 'Mining', 'Municipalities',
>     'Ports/Marine Services', 'Transportation')),
>
> and I want to remove Municipalities for the more general Government.

Melvin is saying to:
1. create a table named valid_industry,
2. populate it with the valid industries,
3. create an FK constraint on your main table's industry column to
valid_industry.industry, and then
4. drop the constraint invalid_industry.

--
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