Bits of .NET

Collecting multiple rows into one comma-separated string used to require cursors. STRING_AGG does it in one line.

Basic Usage:

-- Get all tags for each post
SELECT 
    PostId,
    STRING_AGG(TagName, ', ') AS Tags
FROM PostTags
GROUP BY PostId;

-- Result:
-- PostId  Tags
-- 1       CSS, HTML, JavaScript
-- 2       SQL, Database, Performance

With Ordering:

SELECT 
    DepartmentId,
    STRING_AGG(EmployeeName, ', ' ORDER BY EmployeeName) AS Employees
FROM Employees
GROUP BY DepartmentId;

With Distinct:

-- Remove duplicates first
SELECT 
    PostId,
    STRING_AGG(DISTINCT TagName, ', ') AS UniqueTags
FROM PostTags
GROUP BY PostId;

Available in: SQL Server 2017+, PostgreSQL 9.0+, MySQL 8.0+

No more ugly cursor loops!