MySQL change a column to unique

Question

I have a database table that saved users profile information. Sometimes when users register, they get duplicated with an extra column with same records, sometimes not.

So, I wonder if I put Unique on the column Email to make sure the user don't dup when register.

I think it should be something like this:

ALTER TABLE users ADD UNIQUE idx_row_unique(email);

But in case the Unique give error, how do I undo it?

Just scare that after I change it, I don't know how to undo it.

GeorgeVremescu · Accepted Answer · 2013-02-11 20:35:06Z

2

If there are duplicate emails, the alter table should fail. So you're safe with that!

answered Feb 11, 2013 at 20:35

GeorgeVremescu

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3 Comments

Ya Fa Su Over a year ago

Even like the function force the database to create 2 column identical?

Ya Fa Su Over a year ago

Because I don't why sometimes, my function register saved with the user 2 times identical. So, I want to check it, and Keep one and remove the other.

GeorgeVremescu Over a year ago

So, if now you have 2 times the same mail in your field, the alter table statement will fail. For the future, if you have a function that saves the data in the database, you need to change that to consider the new conditions.

tjfo · Accepted Answer · 2013-02-11 20:36:37Z

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I'd export the table structure and data first. That way if you need to put it back, you have the SQL right there.

answered Feb 11, 2013 at 20:36

tjfo

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2 Comments

Ya Fa Su Over a year ago

is there a way to export it? I didn't create the database

tjfo Over a year ago

If you have access to phpMyAdmin for the database there is an export feature. There is no way that I know of to do it through code.

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