In some occasions it is necessary to concatenate data from a number of rows into a single row.
Using HR.DEMO table as an example , we want to retrieve a list of employees for each department.
Base Data :
Desired Output :
One approach is to write a specific function to solve the problems.
The function can the be incorporated into a query . For example :
On Oracle Database 10g we can use the following query:
Oracle Database 11g Release 2 has an build-in function – LISTAGG.
LISTAGG is an aggregate function that can optionally be used as an analytic (i.e. the optional OVER() clause). The following elements are mandatory:
- the column or expression to be aggregated;
- the WITHIN GROUP keywords;
- the ORDER BY clause within the grouping.
For example :
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