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Finding missing records in SQL table

Posted on 2014-09-04
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Last Modified: 2014-11-28
The table stored in mySQL database contains the ID column, which is a number between 2000000 and 4000000. The numbers are ordered and sequential (increment by 1). I need a SQL query which can loop through this range and find all missing records (the database should contain 2000000 records, but currently contains only 1800000).

Thank you, experts!
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Question by:cyber-33
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LVL 32

Expert Comment

by:Daniel Wilson
ID: 40303733
Create a table of numbers, 2 million to 4 million.
create table numbers (N bigint);
then do a loop that inserts the numbers you need.

Next select the numbers that have no counterpart in your table.

Select N from numbers where not exists (Select ID from MyTable where ID = N);
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Author Comment

by:cyber-33
ID: 40303742
I would need a script that populates the new table you are suggesting.

Also, there should be a simpler way finding the missing records by using a cursor and a single query.
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LVL 25

Accepted Solution

by:
Tomas Helgi Johannsson earned 500 total points
ID: 40303886
Hi!

Try this sql to find the missing values (gaps) in your sequence.

SELECT a.id+1 AS start, MIN(b.id) - 1 AS end
    FROM mytable AS a, mytable AS b
    WHERE a.id < b.id
    GROUP BY a.id
    HAVING start < MIN(b.id)

Open in new window


Regards,
       Tomas Helgi
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Author Comment

by:cyber-33
ID: 40304311
Tomas, I tried running the query but it never came back... Can you please explain the logic behind it?
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LVL 110

Expert Comment

by:Ray Paseur
ID: 40305885
... there should be a simpler way finding the missing records
Really?  How often do you need to do this?  If it's more than once, there is something suspicious about the overall design.  My sense is that any solution would be the best solution.  And with only two million records it's not a large process.

Please post the CREATE TABLE statement and show us some of your test data.  Armed with that we can almost certainly give you a tested-and-working code sample.
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