MySQL数据库

SELECT FieldA
     , GROUP_CONCAT(FieldB ORDER BY FieldB SEPARATOR ',') AS FieldBs
  FROM TableName
 GROUP BY FieldA
 ORDER BY FieldA;

Oracle和 db2

SELECT FieldA
     , LISTAGG(FieldB, ',') WITHIN GROUP (ORDER BY FieldB) AS FieldBs
  FROM TableName
 GROUP BY FieldA
 ORDER BY FieldA;

PostgreSQL数据库

SELECT FieldA
     , STRING_AGG(FieldB, ',' ORDER BY FieldB) AS FieldBs
  FROM TableName
 GROUP BY FieldA
 ORDER BY FieldA;

SQL服务器

SQL Server 2017及以上版本和Azure SQL

SELECT FieldA
     , STRING_AGG(FieldB, ',') WITHIN GROUP (ORDER BY FieldB) AS FieldBs
  FROM TableName
 GROUP BY FieldA
 ORDER BY FieldA;

SQL Server ≤ 2016（包括CTE以鼓励DRY principle）

WITH CTE_TableName AS (
       SELECT FieldA, FieldB
         FROM TableName)
SELECT t0.FieldA
     , STUFF((
       SELECT ',' + t1.FieldB
         FROM CTE_TableName t1
        WHERE t1.FieldA = t0.FieldA
        ORDER BY t1.FieldB
          FOR XML PATH('')), 1, LEN(','), '') AS FieldBs
  FROM CTE_TableName t0
 GROUP BY t0.FieldA
 ORDER BY FieldA;

SQLite

排序需要CTE或子查询

WITH CTE_TableName AS (
       SELECT FieldA, FieldB
         FROM TableName
        ORDER BY FieldA, FieldB)
SELECT FieldA
     , GROUP_CONCAT(FieldB, ',') AS FieldBs
  FROM CTE_TableName
 GROUP BY FieldA
 ORDER BY FieldA;

无需订购

SELECT FieldA
     , GROUP_CONCAT(FieldB, ',') AS FieldBs
  FROM TableName
 GROUP BY FieldA
 ORDER BY FieldA;

从SQL Server 2017开始，可以使用STRING_AGG函数，这大大简化了逻辑：

select FieldA, string_agg(FieldB, '') as data
from yourtable
group by FieldA

查看SQL Fiddle演示
在SQL Server中，您可以使用FOR XML PATH来取得结果：

select distinct t1.FieldA,
  STUFF((SELECT distinct '' + t2.FieldB
         from yourtable t2
         where t1.FieldA = t2.FieldA
            FOR XML PATH(''), TYPE
            ).value('.', 'NVARCHAR(MAX)') 
        ,1,0,'') data
from yourtable t1;

查看SQL Fiddle演示

在SQL Server 2017中添加了STRING_AGG：

SELECT t.name,STRING_AGG (c.name, ',') AS csv
FROM sys.tables t
JOIN sys.columns c on t.object_id = c.object_id
GROUP BY t.name
ORDER BY 1

此外，STRING_SPLIT适用于相反的情况，并且在SQL Server 2016中可用

这可能对某些人也很有用，例如，用于数据分析和数据概要类型的目的。（例如，不按分组）。
在SQL Server 2017 STRING_AGG之前，函数已存在。
(i.e.仅返回一行..）

SELECT DISTINCT
    SUBSTRING(
        STUFF((
            SELECT DISTINCT ',' + [FieldB] 
            FROM tablename 
            ORDER BY 1 
            FOR XML PATH(''), TYPE).value('.', 'NVARCHAR(MAX)') 
        , 1, 0, '')
    , 2, 9999)
FROM tablename

它返回逗号分隔的值-例如“A，B”。