Alternative to STRING_AGG in SQL

This is the exploration of STRING_AGG in SQL alternatives across various database systems.

The SQL STRING_AGG function is used to merge the values of a column from one or more rows into a single string separated by the use of a specified delimiter. This may be included in many modern databases but does not exist in some older versions or database systems. In that case, you require alternative solutions for the same task.

Table of Contents

• Introduction to STRING_AGG
  • What is STRING_AGG?
  • Use cases of STRING_AGG
• Alternative to STRING_AGG in SQL
  • Using FOR XML PATH in SQL Server
  • Using LISTAGG in Oracle
  • Using GROUP_CONCAT in MySQL
  • Using Recursive Queries for Compatibility
• Examples of Alternatives to STRING_AGG in SQL
  • Concatenating Values in SQL Server
  • Concatenating Values in MySQL
  • Concatenating Values in PostgreSQL
• Performance Considerations
• Conclusion
• FAQs

Introduction to STRING_AGG

What is STRING_AGG?

STRING_AGG is concatenating multiple values into a singular string separated with a delimiter to be used especially in creating comma-separated lists or aggregations of text types of data, etc.

Syntax:

SELECT STRING_AGG(column_name, ', ') AS concatenated_result
FROM table_name;

Use Cases of STRING_AGG

• Outputting a value list from several rows for some reporting purposes, etc.
• Aggregation of text data for visualization.
• Grouping of several rows into one output for easier reading.

Alternative to STRING_AGG in SQL

1. Using FOR XML PATH in SQL Server

SQL Server provides the FOR XML PATH method to concatenate rows into a single string.

Example:

SELECT STUFF((
    SELECT ', ' + column_name
    FROM table_name
    FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)'), 1, 2, '') AS concatenated_result;

2. Using LISTAGG in Oracle

Oracle’s LISTAGG function is a direct equivalent to STRING_AGG.

Example:

SELECT LISTAGG(column_name, ', ') WITHIN GROUP (ORDER BY column_name) AS concatenated_result
FROM table_name;

3. Using GROUP_CONCAT in MySQL

MySQL offers the GROUP_CONCAT function for similar functionality.

Example:

SELECT GROUP_CONCAT(column_name SEPARATOR ', ') AS concatenated_result
FROM table_name;

4. Using Recursive Queries for Compatibility

For databases without built-in aggregation functions, recursive queries can be used as an alternative.

Example:

WITH RecursiveCTE AS (
    SELECT id, CAST(column_name AS VARCHAR(MAX)) AS concatenated_result
    FROM table_name
    WHERE id = 1
    UNION ALL
    SELECT t.id, CONCAT(r.concatenated_result, ', ', t.column_name)
    FROM table_name t
    INNER JOIN RecursiveCTE r ON t.id = r.id + 1
)
SELECT concatenated_result
FROM RecursiveCTE
WHERE id = (SELECT MAX(id) FROM table_name);

Examples of Alternative to STRING_AGG in SQL

1. Concatenating Values in SQL Server

SELECT STRING_AGG(column_name, ', ') AS concatenated_result
FROM table_name;
-- Alternative:
SELECT STUFF((
    SELECT ', ' + column_name
    FROM table_name
    FOR XML PATH(''), TYPE
).value('.', 'NVARCHAR(MAX)'), 1, 2, '') AS concatenated_result;

2. Concatenating Values in MySQL

SELECT GROUP_CONCAT(column_name SEPARATOR ', ') AS concatenated_result

FROM table_name;

3. Concatenating Values in PostgreSQL

SELECT array_to_string(array_agg(column_name), ', ') AS concatenated_result

FROM table_name;

Performance Considerations

When using alternative methods, consider the following:

• Data Size: Large datasets can impact the performance of concatenation functions.
• Indexing: Proper indexing can improve the performance of recursive queries or subqueries.
• Memory Usage: Recursive queries may consume more memory, especially with large datasets.

Conclusion

While STRING_AGG is convenient, there are several alternatives to this function when the database doesn’t support it. Depending on the database system you are using, you could use methods such as FOR XML PATH, GROUP_CONCAT, LISTAGG, or even recursive queries. Each method has its pros and cons, depending on your use case and the compatibility of your database.

FAQs

STRING_AGG(column_name, ', ') WITHIN GROUP (ORDER BY column_name)