# Re: [PERFORM] Insert performance (OT?)

```Yves Vindevogel wrote:
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`Hi,`
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Suppose I have a table with 4 fields (f1, f2, f3, f4)
I define 2 unique indexes u1 (f1, f2, f3) and u2 (f1, f2, f4)

I have 3 records
A, B, C, D (this will be inserted)
A, B, C, E (this will pass u2, but not u1, thus  not inserted)
A, B, F, D (this will pass u1, but not u2, thus not inserted)
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Are you saying you want to know whether they will be inserted before you try to do so?
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```Now, for performance ...

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I have tables like this with 500.000 records where there's a new upload of approx. 20.000 records. It is only now that we say index u2 to be necessary. So, until now, I did something like insert into ... select f1, f2, f2, max(f4) group by f1, f2, f3
```That is ok ... and also logically ok because of the data definition
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I'm confused here - assuming you meant "select f1,f2,f3", then I don't see how you guarantee the row doesn't alredy exist.
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I cannot do this with 2 group by's. I tried this on paper and I'm not succeeding.
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I don't see how you can have two group-by's, or what that would mean if you did.
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So, I must use a function that will check against u1 and u2, and then insert if it is ok.
```I know that such a function is way slower that my insert query.
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So - you have a table, called something like "upload" with 20,000 rows and you'd like to know whether it is safe to insert them. Well, it's easy enough to identify which ones are duplicates.
```
SELECT * FROM upload JOIN main_table ON u1=f1 AND u2=f2 AND u3=f3;
SELECT * FROM upload JOIN main_table ON u1=f1 AND u2=f2 AND u3=f4;

Are you saying that deleting these rows and then inserting takes too long?

--
Richard Huxton
Archonet Ltd