List Aggregation in SQL Server
SQL Server provides a powerful set of functions for data aggregation, including the ability to concatenate values from multiple rows into a single comma-separated string. Mastering this aggregation method is critical for a variety of data aggregation and presentation tasks.
To achieve the same functionality as Oracle's LISTAGG function in SQL Server, you can use the STRING_AGG function. Introduced in SQL Server 2017, this function allows concatenating strings within a group.
Example
Consider the following dataset:
字段 A | 字段 B |
---|---|
1 | A |
1 | B |
2 | A |
Query:
SELECT FieldA, STRING_AGG(FieldB, ',') WITHIN GROUP (ORDER BY FieldB) AS FieldBs FROM TableName GROUP BY FieldA ORDER BY FieldA;
Result:
字段 A | FieldBs |
---|---|
1 | A, B |
2 | A |
The STRING_AGG function with the WITHIN GROUP clause ensures that values are concatenated within each group grouped by FieldA. The ORDER BY clause in an aggregate specifies the order in which values should be listed.
For SQL Server versions prior to 2017, you can use a combination of CTE (common table expression) and STUFF functions to achieve the same result. However, for simplicity and compatibility with newer versions, the STRING_AGG function is the recommended solution.
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