How Can I Efficiently Concatenate and Group Rows in Oracle?

Concatenating and Grouping Rows in Oracle: Revisiting Row Manipulation and Aggregation Techniques

In the realm of data manipulation and aggregation, Oracle offers a versatile set of functions that enable efficient processing of large datasets. One common task involves concatenating and grouping multiple rows to achieve a desired result.

Consider the following scenario: Given a table with columns NAME and GROUP_NAME, you aim to transform the data into a new table where rows are grouped based on GROUP_NAME and the corresponding NAME values are concatenated within each group.

One approach for this task is to leverage the SYS_CONNECT_BY_PATH function, as demonstrated in the provided SQL statement. This approach iteratively builds a concatenated string by connecting row values within each group.

However, for more advanced scenarios, the LISTAGG function offers a sophisticated solution. Supported in Oracle 11g and later, LISTAGG allows for efficient aggregation of values within each group, separating them with a specified delimiter (such as a comma).

SELECT group_name,
       LISTAGG(name, ', ') WITHIN GROUP (ORDER BY GROUP) "names"
FROM name_table
GROUP BY group_name

For earlier versions of Oracle that lack LISTAGG, consider utilizing analytical functions such as ROW_NUMBER and SYS_CONNECT_BY_PATH to achieve row concatenation and grouping.

select grp,
    ltrim(max(sys_connect_by_path
       (name, ',' )), ',')
        scbp
  from (select name, grp,
            row_number() over
           (partition by grp
            order by name) rn
         from tab
          )
start with rn = 1
connect by prior rn = rn-1
and prior grp = grp
  group by grp
  order by grp

By exploring these techniques, you can effectively concatenate and group rows in Oracle, handling complex data manipulations and aggregation requirements with ease.

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