How Can I Efficiently Combine Multiple Oracle Rows into a Single Comma-Separated String?

Oracle Row Aggregation: Creating Comma-Separated Strings

A frequent task in Oracle database management involves consolidating data from multiple rows into a single string, separated by commas. This guide explores efficient methods using built-in functions, eliminating the need for complex custom procedures.

Utilizing Built-in Functions

Oracle offers powerful built-in functions designed for this purpose, providing simpler and often more performant solutions than custom PL/SQL functions.

• LISTAGG (Oracle 11.2 and later): This function directly aggregates rows into a comma-separated string. The ORDER BY clause within the WITHIN GROUP specification controls the order of the concatenated values.

SELECT LISTAGG(table_name, ', ') WITHIN GROUP (ORDER BY table_name)
FROM USER_TABLES;

• WM_CONCAT (Older Oracle Versions): For databases lacking LISTAGG support, WM_CONCAT offers similar functionality.

SELECT WM_CONCAT(table_name)
FROM USER_TABLES;

Advanced Techniques and Considerations

• Partitioning: For partitioned data, use the OVER PARTITION BY clause to group results within each partition.
• Custom Delimiters: Both LISTAGG and WM_CONCAT allow specifying a delimiter other than a comma.
• Null Value Handling: Null values are typically omitted. Use NULLIF to replace nulls with an empty string or a specific character if needed.

Summary

Oracle's built-in functions provide efficient and flexible solutions for concatenating multiple rows into single comma-separated strings. This approach simplifies code and optimizes query performance compared to custom PL/SQL solutions.

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