Prevent duplicated row SQL

Question

Let me explain in the current context:

I have a tokens table which contains two columns: name and token.

For example, a user named "John" can be assigned an "updated" token.

However, I don't want to have two rows containing "John", "updated". However, there may be one line containing "Mathew", "updated", so primary keys cannot be used.

Is it possible to do this without executing two statements? Thank you in advance.

You can have a primary key made up of both `name` and `token`. — GriffeyDog, Apr 28 '20 at 20:25
Do you want to prevent *insertion* of duplicate rows, or do you want to remove duplicate rows when *querying* the table? — The Impaler, Apr 28 '20 at 20:29

score 2 · Answer 1 · answered Apr 28 '20 at 20:25

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What you are looking at is making both name and token unique, you could add a line:

unique(name, token);

Or making the primary key of the table being the pair (name, token) by writing this:

primary key(name, token);

By doing this, you will only accept 1 unique row of both name and token.

answered Apr 28 '20 at 20:25

CodeCop

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You may be right. Maybe the OP wanted to prevent "insertion" of duplicate rows. Let's ask for clarification. – The Impaler Apr 28 '20 at 20:29

score 0 · Answer 2 · answered Apr 28 '20 at 20:22

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You can use DISTINCT. For example:

select distinct name, token from tokens

DISTINCT is typed right after SELECT and applies to the whole row. It removes identical rows, showing a single one per combination.

answered Apr 28 '20 at 20:22

The Impaler

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score 0 · Answer 3 · answered Apr 28 '20 at 20:31

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Best solution would be to creat unique key from this columns. One unique key should be applied to both columns at the same time. It will prevent adding data or updating data in database which could cause duplication

answered Apr 28 '20 at 20:31

Huseyn Zeynalov

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Prevent duplicated row SQL

3 Answers3