How to get only repeated records in a table?

问题

I couldn't figure out how better to ask this question, so my searches became desperate.

I have a table with three columns(Column1, Column2, Column3). There are lots of records consisted of different and same values in it. I want to get only the exactly same records as column1, column2 and column3 values. How can I get them in the fastest query in general SQL? And especially HSQLDB?

Besides, if my table has 4 columns (+ Column4) but still I need same records of column1,column2 and column3 values. Query must change or will be same?

Example;

-------------------------------
| Column1 | Column2 | Column3 |
|    1    |    2    |   3     |  <-- A
|    2    |    2    |   30    |  <-- B
|    3    |    3    |   10    |
|    4    |    12   |   3     |  <-- C
|    1    |    3    |   3     |
|    1    |    4    |   3     |
|    1    |    5    |   3     |
|    4    |    12   |   3     |  <-- C
|    2    |    2    |   30    |  <-- B
|    1    |    2    |   3     |  <-- A
|    4    |    12   |   3     |  <-- C
-------------------------------

So I need to select all A,B and C records. The result should be;

-------------------------------
| Column1 | Column2 | Column3 |
|    1    |    2    |   3     |  <-- A
|    2    |    2    |   30    |  <-- B
|    4    |    12   |   3     |  <-- C
|    4    |    12   |   3     |  <-- C
|    2    |    2    |   30    |  <-- B
|    1    |    2    |   3     |  <-- A
|    4    |    12   |   3     |  <-- C
-------------------------------

-Result omitted completely different records-

回答1:

Get them by grouping in combination with a HAVING clause. This should also work in HSQLDB. The HAVING clause removes all data from result a rows isn't contained multiple. When you have a table with 4 columns you have to adopt the statement.

SELECT Column1,Column2,Column3 FROM Table GROUP BY Column1,Column2,Column3 HAVING COUNT(*)>1

EDIT: edited to get all rows

SELECT x.* FROM Table x INNER JOIN (
    SELECT Column1,Column2,Column3 FROM Table GROUP BY Column1,Column2,Column3 HAVING COUNT(*)>1
) y ON x.Column1=y.Column1 AND x.Column2=y.Column2 AND x.Column3=y.Column3

回答2:

SELECT Column1, Column2, Column3, count(*) from myTable
GROUP BY Column1, Column2, Column3

You can omit the Count(*) if you don't care about the count. Is this what you want?

It was a bit difficult to understand what you want. Could you please give an example of you desired output result?

来源：https://stackoverflow.com/questions/7105618/how-to-get-only-repeated-records-in-a-table

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sql

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