Oracle: Combining Rows into Comma-Separated Lists
Frequently, data manipulation requires aggregating multiple rows into a single, comma-delimited string. Oracle offers several methods to accomplish this:
Method 1: LISTAGG (Oracle 11.2 and later)
The LISTAGG
function (available from Oracle 11.2 onwards) efficiently concatenates rows using a specified delimiter. Its syntax is:
LISTAGG(expression, delimiter [, separator]) WITHIN GROUP (ORDER BY order_expression)
Example: Generating a comma-separated list of country names from a countries
table:
SELECT LISTAGG(country_name, ', ') WITHIN GROUP (ORDER BY country_name) FROM countries;
Method 2: WM_CONCAT (Oracle versions prior to 11.2)
For older Oracle databases (before 11.2), the WM_CONCAT
function provides a similar capability:
SELECT WM_CONCAT(country_name) FROM countries;
Method 3: Custom PL/SQL Function
Should neither LISTAGG
nor WM_CONCAT
suffice, a custom PL/SQL function offers a flexible solution. This allows for tailored concatenation logic, as demonstrated in the example provided using loops and string concatenation.
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