Is there an Oracle SQL query that aggregates multiple rows into one row?

Question

I have a table that looks like this:

A 1 
A 2 
B 1 
B 2

And I want to produce a result set that looks like this:

A 1 2 
B 1 2

Is there a SQL statement that will do this? I am using Oracle.

Related questions:

• Returning multiple rows from a single row My question is close to the opposite of this question.
• Use LINQ to concatenate This is exactly what I want to do, but without LINQ.

Answer 1

See similar question advice-using-pivot-table-in-oracle

Answer 2

User defined aggregate functions: http://www.adp-gmbh.ch/ora/sql/user_def_agg.html

Just copy/paste and use it. Works on 9i.

Answer 3

It depends on the version of Oracle you're using. If it supports the wm_concat() function, then you can simply do something like this:

SELECT field1, wm_concat(field2) FROM YourTable GROUP BY field2;

wm_concat() basically works just like group_concat() in MySQL. It may not be documented, so fire up ye olde sqlplus and see if it's there.

If it isn't there, then you'll want to implement something equivalent yourself. You can find some instructions on how to do this in the string aggregation page at oracle-base.com.

Answer 4

Try something like :

SELECT
    field1,
    RTRIM(REPLACE(REPLACE(XMLAgg(XMLElement("x", field2) ORDER BY field2), '<x>'), '</x>', ' ')) AS field2s
  FROM yourTable
  GROUP BY field1

Freely inspired by an answer found in this Oracle forum.

EDIT: this solution proved very resources intensive with requests involving something like 10⁵ rows. I ended up replacing this by custom aggregate functions as suggested by John.

Answer 5

In Oracle 10g+:

SELECT  *
FROM    (
        SELECT  *
        FROM    mytable
        MODEL
        PARTITION BY
                (grouper)
        DIMENSION BY
                (ROW_NUMBER() OVER (PARTITION BY grouper ORDER BY id) AS rn)
        MEASURES
                (val, val AS group_concat, 0 AS mark)
        RULES SEQUENTIAL ORDER (
                group_concat[rn > 1] ORDER BY rn = group_concat[CV() - 1] || ', ' || val[CV()],
                mark[ANY] ORDER BY rn = PRESENTV(mark[CV() + 1], 0, 1)
                )
        )
WHERE   mark = 1
ORDER BY
        grouper

See this article in my blog for explanations:

• GROUP_CONCAT in Oracle 10g

Answer 6

Mac, you've got a magical solution!!!