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Optimizing String Aggregation in SQL Azure
Efficiently combining strings from multiple rows into a single row is a frequent data manipulation task. While some aggregation methods prove inadequate, optimal solutions exist to overcome this challenge.
The Best Approach for SQL Azure
SQL Azure's lack of CLR-defined aggregate functions necessitates alternative strategies. The following Transact-SQL approach provides an efficient solution:
<code class="language-sql">WITH Partitioned AS ( SELECT ID, Name, ROW_NUMBER() OVER (PARTITION BY ID ORDER BY Name) AS NameNumber, COUNT(*) OVER (PARTITION BY ID) AS NameCount FROM dbo.SourceTable ), Concatenated AS ( SELECT ID, CAST(Name AS nvarchar(max)) AS FullName, Name, NameNumber, NameCount FROM Partitioned WHERE NameNumber = 1 UNION ALL SELECT P.ID, CAST(C.FullName + ', ' + P.Name AS nvarchar(max)), P.Name, P.NameNumber, P.NameCount FROM Partitioned AS P INNER JOIN Concatenated AS C ON P.ID = C.ID AND P.NameNumber = C.NameNumber + 1 ) SELECT ID, FullName FROM Concatenated WHERE NameNumber = NameCount;</code>
Detailed Explanation:
This solution employs a three-part process:
ID
partition, ordered alphabetically by Name
, using ROW_NUMBER() OVER (PARTITION BY ID ORDER BY Name)
.Name
values based on the assigned row numbers.NameNumber
within each partition, yielding a single concatenated string per ID
.Note: This query assumes grouping by ID
and ascending alphabetical order of strings. Adaptations may be needed depending on your specific data structure and requirements. The nvarchar(max)
cast ensures sufficient string length for large concatenated results.
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