列出连接

部分归功于这个 SO 答案。

List Concatenation 通过将值组合为每个组的单个字符串来聚合列或表达式。可以指定用于分隔每个值的字符串（省略时为空白或逗号）以及结果中值的顺序。虽然它不是 SQL 标准的一部分，但每个主要的关系数据库供应商都以自己的方式支持它。

MySQL

SELECT ColumnA
     , GROUP_CONCAT(ColumnB ORDER BY ColumnB SEPARATOR ',') AS ColumnBs
  FROM TableName
 GROUP BY ColumnA
 ORDER BY ColumnA;

Oracle 和 DB2

SELECT ColumnA
     , LISTAGG(ColumnB, ',') WITHIN GROUP (ORDER BY ColumnB) AS ColumnBs
  FROM TableName
 GROUP BY ColumnA
 ORDER BY ColumnA;

PostgreSQL

SELECT ColumnA
     , STRING_AGG(ColumnB, ',' ORDER BY ColumnB) AS ColumnBs
  FROM TableName
 GROUP BY ColumnA
 ORDER BY ColumnA;

SQL Server

SQL Server 2016 及更早版本

（包括 CTE 以鼓励 DRY 原则 ）

  WITH CTE_TableName AS (
       SELECT ColumnA, ColumnB
         FROM TableName)
SELECT t0.ColumnA
     , STUFF((
       SELECT ',' + t1.ColumnB
         FROM CTE_TableName t1
        WHERE t1.ColumnA = t0.ColumnA
        ORDER BY t1.ColumnB
          FOR XML PATH('')), 1, 1, '') AS ColumnBs
  FROM CTE_TableName t0
 GROUP BY t0.ColumnA
 ORDER BY ColumnA;

SQL Server 2017 和 SQL Azure

SELECT ColumnA
     , STRING_AGG(ColumnB, ',') WITHIN GROUP (ORDER BY ColumnB) AS ColumnBs
  FROM TableName
 GROUP BY ColumnA
 ORDER BY ColumnA;

SQLite

没有订购：

SELECT ColumnA
     , GROUP_CONCAT(ColumnB, ',') AS ColumnBs
  FROM TableName
 GROUP BY ColumnA
 ORDER BY ColumnA;

订购需要子查询或 CTE：

  WITH CTE_TableName AS (
       SELECT ColumnA, ColumnB
         FROM TableName
        ORDER BY ColumnA, ColumnB)
SELECT ColumnA
     , GROUP_CONCAT(ColumnB, ',') AS ColumnBs
  FROM CTE_TableName
 GROUP BY ColumnA
 ORDER BY ColumnA;