CODEWITHSUNDEEP
c#mysql
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Reputation:

How can I prevent duplicate rows in MySql?

I seven columns in my MySQL table. Four of these are called A B C D.

Assume that I already have values 1 ,2 ,3 ,4. How can I prevent a duplicate combination from being added.

Upvotes: 0

Views: 237

Answers (3)

TidyDev
TidyDev

Reputation: 3668

In MySql, you can create a unique key that is a combination of several columns.

ALTER TABLE <nameOfTable> ADD UNIQUE KEY (A, B, C, D);

However it should be noted that there could be a large performance impact if these fields are storing text or other long values.

Upvotes: 0

Sam
Sam

Reputation: 597

Why don't you simply make a unique key for A, B, C, D

ALTER TABLE <tablename> ADD UNIQUE KEY (A, B, C, D);

Upvotes: 2

Alec
Alec

Reputation: 9078

You can set a MySQL field to UNIQUE, but not a combination of fields, as far as I know.

So, first do a simple query to see if the combination A=1, B=2, C=3, D=4 already exists. If not, add it, otherwise prompt the user with an error.

Upvotes: -1

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